Had a little problem driving to work today.

I was sitting on about 65 when the car starts to lose power so I stop on the side of the road and the motor dies. Try to start the car and motor dies again. Start the car and rev it, take foot off, dies again. Get out of car and check all earth connections for the sake of it, get in and start car... dies again.

Fuel pump sounds a bit funny. So I get out, reach under and just check connections. Filled the tank on Wednesday but I thought I'd check just in case. Undo cap, won't come off... give it a yank and it comes off with a 'pop'... the suction on the cap was very strong Put cap back on, start car, everything's fine.

Seems the tank isn't breathing properly

Oz Minis run a sealed cap. The breather is connected onto top of tank, it's a black plastic line that on earlier cars simply went down thru the boot floor. Pull it out and blow thru it with air or a garden hose.
Cooper S and Clubby GT had 2 lines.
Later cars had the breather line connected to a steel pipe that ran up to the engine bay next to the brake pipe, and was connected to the charcoal canister.
Sounds like yours is blocked. No air in = no fuel out....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Yep... that's what mine is.

Stuck a bit of tissue in the end of the pipe in the engine bay and reversed the flow of the vacuum to blow through it and the tissue didn't move and I've probably go no hope sticking something down the pipe to push whatever it is out. The pipe may even be squashed somewhere.

So sticking the hose through the floor and sticking one of these on the end is fine?