Pressure in the fuel system?

Having read all through the forum i think i might have some idea whats going on but then again.
I have been using the car daily for the last few years without any problems but since moving house and hauling quite a few boxes around in it there seems to be a pressure build up in the tank.
When i get the car out of the garage in the morning there is a strong smell of fuel but without any tell tale signs of leaking.Driving to and from work there is no running problems as far as i can tell.When i went to fuel up the car there was a "wooshing" sound from the tank which i put down to the fuel level being low.After driving about 18 miles home i decided to see if there was still pressure in the tank,taking the fuel cap off resulted in a small amount of fuel spitting from the fuel filler!!
The smell of fuel is strong when you stick your head close to the drivers side rear wheel but there is no signs of fuel leaking??
Will investigate over the weekend but just thought that you might be able to point me in the right direction.

Thanks
Sean

probably the tank has vacuum rather than pressure, check all the breathers though either way. there should be a thin hose sticking out of the tank somewhere that is open to air

Cheers John.I will check all the breathers and hopefully that should sort it,fingers crossed.

Did you mange to sort this? I have the exact same problem only now the car won't let me fill it with petrol it gets about £10 from empty and the fuel starts come through the breather pipe back into the filler neck like its full? Checked and I only have the 1 breather connected, the one the fuel coming back through. Tried to attach a breather as the hose is there for the one at the back of the tank but I can't get in(the outlets on the tank have rubber caps on). What's odd though is the car has always had this set up an it's never been a problem, now it jut won't take fuel!
Cheers
Jamie