Heavily-armed Special Forces soldiers driving specially adapted and armoured civilian vehicles will patrol Britain's streets in a bid to thwart an Islamic State atrocity over the Bank Holiday Weekend.

Security sources disclosed last night that elite troops will mingle with revellers and tourists at sites considered most at risk of a terrorist attack. But the male and female personnel will remain incognito unless called upon to intercept any jihadis.

A security source told The Mail on Sunday last night: 'They will be casually dressed with their weapons hidden beneath their clothes. They won't be in traditional military vehicles either.

A girl has her photo taken with Armed Police at V Festival in Weston Park, Staffordshire

'Recently, a company of Special Forces Support Group troops completed a live firing exercise using Civilian Armoured Vehicles and they will be called upon.

'These are regular cars but with special adaptations such as armour-plated doors and reinforced bullet-proof windows to assist them in an urban close quarter battle scenario,' the source added.

'The other troops who have been called up for the Bank Holiday Weekend include personnel from the Special Reconnaissance Regiment, who are experts in undercover operations.'

It is understood a list of locations in London and around the UK thought to be the most likely targets for IS is being finalised. This is likely to include airports and major sports stadiums.

'The terrorists are also thought to be planning a 'triple tap' attack – three incidents either simultaneously or shortly afterwards but in the same vicinity,' added the source.

The Ministry of Defence declined to comment last night.