The prime minister has praised the fire service for their work in tackling fires which have broken out all across the country.
Firefighters are still battling to control fires after the hottest April on record created tinderbox conditions in many parts of the UK.
The hottest April on record, with only 52% of the usual April rainfall, has created tinderbox conditions.
Fires continue to burn in parts of the Scottish Highlands, Wales, Berkshire, Lancashire and Yorkshire.
Weather forecasters say there is little chance of rain before Thursday.
Crews in Northern Ireland have responded to more than 1,000 gorse and forestry fires over the past four days.
Police are warning they will arrest suspected arsonists, after youths were seen starting fresh fires at Swinley Forest near Crowthorne, Berkshire.
Police in Berkshire said youths were seen starting fresh blazes at Swinley Forest near Bracknell.
Responding to a question from the local Conservative MP, Dr Phillip Lee, Mr Cameron praised firefighters for their work "in this difficult endeavour".
During Prime Minister's Questions, David Cameron praised firefighters for their work "in this difficult endeavour".
He insisted funds would be made available to pay for the cost of the firefighting operation and told the House of Commons: "There are well tried and tested procedures to make sure that central government stands behind local government when there are excessive costs."
Responding to a question from Dr Phillip Lee, Conservative MP for Bracknell, Mr Cameron insisted funds would be made available to pay for the cost of the firefighting operation.
Sixty firefighters in West Yorkshire are at the scene of a massive moor fire near Mytholmroyd.
"There are well tried and tested procedures to make sure that central government stands behind local government when there are excessive costs," he said.
Twelve engines have been sent and smoke is drifting onto the M62.
The UK has seen only 52% of the usual April rainfall, and weather forecasters say there is little chance of rain before Thursday.
Fire crews will spend the day damping down moorland near Halifax.
The situation around the country is rapidly changing as firefighters beat out flames, and other fires are started.
In North Yorkshire, a fire is threatening an industrial estate on the outskirts of Thirsk.
In Mytholmroyd, West Yorkshire, fire crews have been tackling a moor fire which started on Tuesday and burned across 1.5 sq kms of land. A helicopter helped douse the flames with water from a reservoir and crews used small jets, back packs and beaters to put the fire out, which is now smouldering.
Nearby, in Wainstalls, West Yorkshire, firefighters have had to dig into the ground before putting water on the fire as it is deep-seated in peat. The fire, which started on Monday and spread over around 1sq km, is said to be under control.
In the south, there have been fires in Dorset. One heath fire in Wareham Forest on Tuesday night is believed to be malicious, according to the fire service. Fire crews are still at the scene of another, reported on Wednesday afternoon at Canford Heath, near Poole. Its cause is unknown.
In south Wales, hundreds of acres of the Brecon Beacons National Park have been destroyed. Head warden Judith Harvey said there had been many fires in the past three weeks but the latest were burning away some of the best habitat, including heather moorland, bilberry and crowberry. "It's a really devastating scene," she said.
In Lancashire, firefighters are now into their sixth day spent trying to put out fires which have destroyed moorland and woodland near Belmont. Many worked through the night as colleagues took on another moor fire near Ormskirk. Experts have been assessing the environmental impact and fear some areas could take decades to recover.
The unusually warm weather has also affected parts of Scotland. The royal family's Balmoral Estate, where the Queen traditionally spends her summer break, was not immune as fire took hold across a large area of heather and gorse. Highlands and Islands Fire and Rescue Service said there was "a continuing severe risk of further fires occurring" as they turned their attention to fires in Inverkirkaig and Lochailort.
In Northern Ireland, there have been fires in County Down, Tyrone and Armagh, several of which are thought to have been started by arsonists.
Roads leading to the scene of the fire remain closed to the public.
Late on Tuesday night, firefighters were called to a heath fire in Wareham Forest, Dorset.
Firefighters are still damping down the area and Dorset Fire and Rescue Service said it believed the cause was "malicious".
Moorland in Lancashire has been on fire for six days.
Nine crews are at a fire near Belmont, near Bolton, and two engines are at another moor fire near Ormskirk. Experts are assessing the environmental impact, and say some areas could take decades to recover.
A Lancashire Fire and Rescue Service spokesman said: "We are hoping it rains, as the land is so dry."
In Scotland, a large area of heather and gorse was on fire on the Balmoral Estate, the royal family's home north of the border.
Highlands and Islands Fire and Rescue Service said there was "a continuing severe risk of further fires occurring".
In Northern Ireland, there have been fires in County Down, Tyrone and Armagh, several of which are thought to have been started by arsonists.
NI Water has urged the public to avoid walking in the Mourne Mountains while the dry conditions persist.
NI Water has urged the public to avoid walking in the Mourne Mountains while the dry conditions persist.
Water from the Mournes runs into Ben Crom and Silent Valley reservoirs.
Water from the Mournes runs into Ben Crom and Silent Valley reservoirs.
'Ruining scenery'
'Ruining scenery'
Dymphna Gallagher, from NI Water, said: "It is unfortunate that these fires are ruining the beautiful scenery and the quality of raw water flowing into the Silent Valley reservoir. Years of work building up this area have been destroyed in a few short days.
Dymphna Gallagher, from NI Water, said: "It is unfortunate that these fires are ruining the beautiful scenery and the quality of raw water flowing into the Silent Valley reservoir. Years of work building up this area have been destroyed in a few short days."
"It will take a long time and a great deal of work and commitment from those involved in preserving the Mournes to return it to the condition it was in."
The Met Office said April was the hottest on record, with many areas of the UK seeing temperatures 3-5C higher than usual. It was the 11th driest April on record.
The Met Office said April was the hottest on record, with many areas of the UK seeing temperatures 3-5C higher than usual.
It was the 11th driest April on record.
England and Wales have experienced only 21% of its average monthly rainfall for the month and south-east England has been particularly dry.
England and Wales have experienced only 21% of its average monthly rainfall for the month and south-east England has been particularly dry.
But despite the dry weather the Environment Agency said it had no plans to introduce a hosepipe ban this summer.
But despite the dry weather the Environment Agency said it had no plans to introduce a hosepipe ban this summer.
A spokesman said: "We encourage people to use water sensibly all the time. Whenever there are dry periods, there is more pressure put on the system.
"But at the moment, the ground water levels and reservoir levels are relatively high. We feel confident there is enough water to see out spring and summer without restrictions on the public supply."
Have you been affected by fires in your area? Send us your comments using the form below.
Have you been affected by fires in your area? Send us your comments using the form below.
Send your pictures and videos to yourpics@bbc.co.uk or text them to 61124 (UK) or +44 7725 100 100 (International). If you have a large file you canupload here.
Send your pictures and videos to yourpics@bbc.co.uk or text them to 61124 (UK) or +44 7725 100 100 (International). If you have a large file you canupload here.
