As I could do without the expense of buying a new one.

Still works fine and not water is getting in.

Ta!

I think so I had smashed fog light and got failed for that.

Yes it is.
Ebay or local scrappy for replacement.

funnily enough one of my front foglights is completely smashed and it's got through 2 MOT's like that.

I think front fogs aren't part of the tests (rear one is)

Link for all things MOT.

yeah, not because of the lighting aspect but because of the dangerous sharp bits on the car aspect.

Mine got through loads with a cracked headlight, finally had to get it changed on the last one as it had began letting water in.

I used the same garage everytime (if that's relevant?)

Ebay

I don't think so as long as it doesn't affect the beam pattern.
Drive to the garage where you are going to get it tested and ask the examiner to have a quick look.

No, as long as it doesn't effect the beam pattern.

I've mot'ed a few vehicles fine with cracked lenses. If in doubt use some thin black tape over the crack to stop it deflecting the light.