I'm going to Le Mans on Wednesday, crossing via Hull. Had planned to take a 5l fuel can with me so I don't get stranded, but just double checking the T&C's and it specifically states you shouldn't take a fuel can, full or empty. So looks like my options are to buy one when I land and chuck it away before I return, cross my fingers and hope my gauge is accurate (clue: it isn't!), or try and take it and plead ignorance if they find it.

What has anyone else done?

I found a 2litre jerry can on ebay, discrete and enough fuel to get the nearest filling station (probably)

Take it, keep it out of sight and you'll be fine. If customs and imigration search you they are looking for drugs and people and couldn't care less about 5L of fuel.

Make a fuel dipstick and keep it in the car.

Take it with you just pack it away so it's out of sight .