They were overheard celebrating moments after the explosion that blew the plane apart, killing all 224 on board.

The terrorists were heard talking in Birmingham and London accents by spies at GCHQ in Cheltenham.

Trained in Syria and with an electronics background, it is believed they may have had a hand in building the bomb.

The success of the attack could inspire them to target British airports next, a former Special Branch officer warned last night.

GCHQ, the Government’s secret listening centre, picked up “chatter” from extremist groups in Egypt immediately after the Russian plane came down.

The regional accents suggest “a definite and strong link” between British extremists and the attack, according to intelligence sources.

“Terrorists in the Sinai area of Egypt could be heard celebrating,” one source said yesterday.

“A closer analysis of that material has identified London and Birmingham accents among those numerous voices.

“There has also been some internet traffic suggesting that there was British involvement in the attack. This was a very sophisticated, carefully planned operation involving many moving parts.

“We know there are British terrorists in Egypt fighting with members of ISIS. They were trained in Syria and are now hardened terrorists. Some of the Britons have an electronics background and have been developing some very sophisticated bombs.

“They have been experimenting with different-sized charges and different types of explosives but there was nothing prior to this attack to suggest that they were going after airlines.”

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