By David Barrett, Home Affairs Correspondent 12:01AM GMT 08 Mar 2016

Full scale of the migrant crisis revealed for the first time as watchdog reveals 40 migrants a day were reaching British soil

Nearly 40 clandestine migrants a day – many from the Calais “Jungle” - were discovered in Dover and the surrounding area last summer, it has emerged.

More than 3,600 migrants were picked up by the Home Office from July to September in the first official indication of the full scale of migrant crisis’ impact on Britain’s border controls.

Home Office officials last year repeatedly denied that figures were available on the numbers of migrants – both asylum seekers and illegal immigrants – who had reached British soil concealed in lorries or on Channel Tunnel trains.

But figures emerged in a report by the Chief Inspector of Prisons, Peter Clarke, following an inspection of detention facilities at the ports of Dover and Folkestone.

Mr Clarke said 3,663 were held over the three month period.

In the first nine months of 2015 the figure was 4,785, he added, a jump of 126 per cent in the same period in 2014.

The figures include only those migrants discovered by officials at or near the two Dover ports and the true total is thought to be far higher, as many escape detection.

Mr Clarke, the new prisons watchdog, said increases in migrant attempts to cross the Channel “initially overwhelmed” the Home Office’s facilities in Kent.

“In June 2015, there had been a sudden and substantial increase in the number of such migrants coming through the Channel Tunnel in particular,” he said.

“It was clear that the unprecedentedly high number of people arriving from France had led to a strain on the infrastructure.”

Short-term holding facilities at Dover and Folkestone were “wholly unacceptable” with migrants - including children travelling alone – held in a freight shed for up to 21 hours, where they were expected to lie on a concrete floor under dirty blankets.

Many of the migrants were from Eritrea, Sudan and Syria, the report said.

“It is difficult to understand why effective contingency plans were not put in place to cater for the rise in the number of migrants,” said the chief inspector.

It came as the Government announced rail and maritime firms, such as ferry companies, could face fines when migrants are found hiding in their vehicles or vessels.

Current rules mean hauliers can be handed an on-the-spot penalty of up to £2,000 for every stowaway discovered on their vehicle.

Now ministers are considering extending the sanctions to other operators.

A Home Office consultation document said: "We wish to seek views on extending the clandestine civil penalty regime to rail freight wagons and freight shuttle wagons.

"We want to see if this would provide greater balance in the deterrent and build on our existing operational relationship with rail operators."

More than 1,000 clandestine migrants a month reached Britain last summer - Telegraph