Do not go to halfords or motor world or any place like that..
this stuff is designed to be able to sit on a shelf for months and months..
Go to a proper AUTO paint suppliers.. You get it mixed there and then for you much much more in a can and its 10x better finish..
I could get a can posted over to you if you wish.. I go to mine about 3 times a week as I get welding gas, sheet metal and all my fibreglass supplies there..
I pay 9 quid plus VAT for a can and its about 3x times as much as a large halfords can, which is around a tenner anyway.. iirc