DO NOT touch the electrified lines on Underground lines or you could find your blood boiling and your muscles seizing up.

That was the gruesome message being given out in safety talks to children to stop them trespassing on the line on Friday.

The Picadilly line from Cockfosters to Hammersmith is the longest underground track in northern Europe and at its northern end sees high instances of trespassing on the tracks.

A new interactive van called the Rail Display Vehicle (RDV) due to be launched next month, was being trialled in Oakwood on Friday.

The RDV can teach children, teenagers and foreign visitors the proper use of the Tube and dangers if travellers do not follow the rules.

It has a ticket machine, Tube map, CCTV and mock-ups of platform and tracks, a lift and an escalator.

Former teacher Chris Nix, now Transport for London's Safety Partnership's head of learning development, tailors the severity of his message to the age of the child and whether they have been caught on the line already.

He stressed that the Tube is one of the safest forms of travel there is as millions of people use it daily without mishap.

But if it is misused it can be fatal.

"If you get electrocuted there's very little chance you will survive and if you do there will be horrendous injuries."

Mr Nix said Tube lines run on DC current so instead of being thrown clear the opposite would happen.

"It locks every single muscle in your body, you can't breathe, you can't shout and your blood boils," he said.

Visitors can roleplay an emergency situation and learn the proper way to call for help.

"A lot of the time you get these local hero stories but the reality is you could have two deaths instead of one.

"The station staff can get the power off really quickly and then you can effect a rescue safely."

Statistics show that escalators are more dangerous than the lines and the RDV has videos showing what can happen if people misuse them or play pranks on users.

Mr Nix tells of one man who sat on the escalator and did not get up in time losing his trousers and his underwear to the escaltor's metal jaws.

Others have fallen to their deaths or had their feet shredded by going on the escalator with undone shoelaces.

There were 1,588 injuries on the Tube network last year and one death.

The RDV, which is due to launch next month, is one of five vehicles which visit stations and schools.