Would anyone care to try and analyse where it's gone tits-up? 
(bought an emergency long-life cake from Tesco - yuck - but it will have to do!)
I had used a different recipe than usual for a madeira sponge in 8in/20cm square cake tin (only I susbsituted a tablespoon of flour for cocoa like it suggested if you want a chocolately flavour)
SR Flour: 350g (12oz)
Caster Sugar: 285g (10oz)
Butter: 285g (10oz)
Eggs: 5
Milk: 45ml (3 tablespoon)
The mixture itself looked absolutely fine and as it should when it went in the tin. It said to cook it on 150 deg C, for 1 and a half to 2 hours. Well, it rose ok, but just didn't ever cook through. I had it in for 2 hours 10 mins then just gave up. Was soggy and greasy, and just, well, uncooked in the middle. The very outside edges seemed passable (so I ate them!!!)
Does that recipe look fine to you? I haven't had any cake disasters before so don't know what went wrong....