A British historian today said it was time for the Allies to show regret for the bombing of German civilians during the Second World War.

Author and lecturer Dr Mark Connelly said the British powers that be have always drawn a shroud over the bombing tactics of the 1939-45 conflict but should now show public sorrow.

His comments come after a German historian accused the British of deliberately and indiscriminately targeting civilians and were effectively guilty of war crimes.

But Jorg Friedrich's book Der Brand has sparked mixed emotions from his British counterparts with other historians claiming Britain was fighting for its life.

In Der Brand (The Fire: Germany Under Bombardment 1940-45), Mr Friedrich believes a total of 635,000 German civilians were killed during the constant air raids.

He reportedly claims British war leader Winston Churchill had favoured a tactic of bombing the public long before the outbreak of the Second World War and before the air raids by Adolf Hitler's Luftwaffe.

The book is a rare change in style from many accounts by German historians whose books have often been less emotive.

Dr Connelly, whose new book Reaching for the Stars addresses the activities of British bomber command and its public perception, said the book was a sign that Germans are beginning to speak out on their suffering in the war.

He stressed it would be dangerous ground for the Allies to apologise for their activities but that there was scope for public regret.

The University of Kent lecturer added: "The British powers that be have always avoided talking about the bombings.

"We know the German people have already admitted their complicity and perhaps it is time for us to express regret.

"There is no doubt that the bombing of civilians was deliberate and it is extremely interesting as it goes in to the debate of how was a war crime defined then.

"The idea behind it by bomber command was that if Germany could be stopped without invasion then that would save British and Commonwealth lives."

Dr Connelly said there has often been a "schoolyard" argument against Germany that "they started it" and that as long as they were seen as the ones who first broke the rules then it was no holds barred for the Allies.

Dr Connelly said the level of German bombings of Britain and other Allied nations was far less than the retaliation exacted against German cities, including Dresden, where tens of thousands died.

But Dr Adrian Gregory, a historian at Oxford University's Pembroke College, said Germany was guilty of targeting civilians from the very outset of the conflict.

The Nazi regime showed no hesitation in attacking civilians in Warsaw, Poland, and beyond as they stormed across Europe, he said, adding: "The attack on Warsaw (which led to the declaration of war by Britain) was a blatant assault on civilians.

"I have a certain amount of scepticism about high moral positions on behalf of Germany given the behaviour of the German government and Luftwaffe.

"Perhaps there is a question of whether the British government should have had higher moral standards than the Third Reich (in terms of retaliation) but at the time we were fighting for our lives."

Dr Gregory said the bombings also inadvertently quickened the end of the war as many German resources, such as 88mm guns, had to be used to protect cities rather than be deployed on the front lines.

He added: "I think the bombing of civilians is a crime but at the same time we have to acknowledge it makes a real contribution to shortening the war and I do not know if we can ever square that circle."