Going to have a go at sealing the above as the gasket seems ok but want to make sure I have a proper seal.

Bought some Loctite Sealant from Halfords, will it be ok?

Tried to ask an assistant at Halfords but he didn't know.

Reason I'm asking is because most say not suitable for fuel.

 

I think a lot of sealants say 'not suitable for parts continually immersed in fuel', or something like that, which wouldn't really apply to the cover at the top of a fuel tank, as this will get just a few splashes of fuel when you go round corners or when you've just brimmed the tank. The devil's in the detail.