Suzuki Club UK

Not had the Samurai for long but when I last filled it up, I put £20 in and it seemed to be full. I went and paid and when I got back the fuel was spilling out onto the floor.
The tank looks in very good condition and I've checked the 2 pipes on the filler neck. Both seem ok and new. I took the fuel cap off and pulled off the breather pipe. I blew into the pipe just to see if it was blocked and it pushed a bit of fuel out the filler neck (no idea if that's good or bad?!).
Anyone experienced anything like this?

Tank could be rotten / damaged on the top?

The gauge sender unit seal might have gone?

One of the steel return / breather pipes on too of the tank may be damaged?

Tank out job and investigate.