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So just before putting my v8 to winter sleep i filled the tank. Not right to the top of the neck.

Got a call from my mother in law( car is in her garage) to say strong smell of fuel - i went round and fuel was coming out of the key hole of the cap( aftermarket cap) . When i took cap off fuel was up to top of neck
Ran the engine and lever dropped.
Put newly refurbished original cap back on
Looked today - fuel right up again ????
Strange

Heat expansion? Fuel is calibrated at the pumps to reflect a certain temperature. Perhaps it is quite a bit warmer in your Mother's garage and the fuel has expanded. Check and run daily until the gas has finished expanding.

If you have the charcoal cannisters I would worry that the gas has expanded into the cannisters thereby wrecking them especially if you had the sealed N/A system (which you do not as locked gas caps are not sealed). A good warning to others to not fill beyond the first click off unless it was because you are filling too fast (very easy to do with the anti siphon cage in).

Not sure what you mean by charcoal filters?

Its a uk spec car

You won't have them then as UK have open fuel system, not closed.

There are a number of different fuel tank & breather systems used on 7s.

On some tank systems in Oz cars, the breather is on the filler neck, rather than on the tank. As the filler pipe is well below the level of the top of the tank, such systems have a moderate air pocket trapped above the fuel in the tank.

Petrol coming from a cool underground tank will be cool, & will cool this pocket of air. As the air in the pocked warms on a warm day, it will expand quite a bit, & can push fuel out of the filler, if it is not sealed.

It is not just 7s that have this habit. On one occasion I filled my Honda S2000 & went to pay, foolishly before fitting the sealing cap. When I came back to the car just a couple of minutes later, petrol was welling up & out of the filler by expansion of air trapped in a similar pocket in the tank.

You could of course have a pin hole in the filler, breather, or the supply hose from the tank. Be careful of some fuel & oil hoses on the market at the moment. I replaced all my fuel hoses with theoretically good quality hose, [branded Gates} a little while back. This split with in 12 months.

We fitted new hose to the gearbox oil cooler on the 8 just after that. That "quality" hose burst in just 18 kilometres. The local drag race gearbox builder told us to use only hose branded "made in USA" as some manufacturers have started making hose in India &/or Mexico, with disastrous results.

Hasbeen

Hi, Depending on how long you are leaving the car you might want to add some "fuel Stabiliser" Lucas oils have it if you have there stuff in the UK. I have not used it personally but it was recommended to me as I am storing a Lotus Esprit turbo for a friend, its been here a year and now is getting really hard to start, when you open the fuel tank filler the fuel has that old "stale" smell to it!

The other problem with leaving a car standing is condensation in the tank. Naturally this settles below the petrol (higher SG) and helps to rot out the bottom of the tank and can cause very rough starting and running when a slug of water/fuel mix gets pulled into the carbs. I had this long ago and found the filter full of water and rust sludge, drained the tank and the most foul mix came out. I now put half a litre of 99.9% Isopropyl Alcohol in the tank when I lay it up for the winter, this absorbs the water and allows it to be burnt off with the fuel. Never had a problem since using it.

If you fill the tank (not over fill) there will be no water condensation because there will be no (little) air to hold the water vapour. Any condensation will have happened during the shoulder months when the tank is never full (for long). I usually don't drive my car for 4 or 5 months over the winter (used the time to get projects done) and some times added stabiliser and sometimes didn't. It never made any difference over that period of time and always started right away (it is fuel injected). If you're storing for longer like up to a year then it matters. I own a Chevy Volt (Opel Ampera for those of you in Europe) and if the fuel in the tank isn't used in a year it will run the range extender engine to use up the fuel (it has a sensor to measure fuel age). Chevy warns against adding any additives to the gas. The tank is under pressure to prevent any of the lighter components from evaporating thereby extending the life of the gas. People who don't use much gas only keep it quarter filled (in part so they aren't lugging gas around that they aren't using) and add a gallon or two every so often so it doesn't get too old. Even if you only drive EV it will run the engine for ten minutes every 6 weeks to circulate the fluids so you always burn some. That's how they take care of old gas.