We have s Claud Butler Cape Wrath 04 (2010).
Tora with 1 1/8″ steerer.
The FSA headset it came with has rubbish sealing, and lower seals and races just destroyed themselves. 🙁

The overall (widest) diameter of the cups is 50mm, the outer face of the bearing surfaces is 44mm I think.

Suggest me a budget, but properly sealed, headset please…

Have a look here for details on what type of headset you might have

http://singletrackworld.com/forum/topic/integrated-headset-bearings

You may well find some better quality fsa bearings that will fit the cup.

Otherwise I’ve always found cane creek last well.

Oh Nora, that’s complex….

It can be complicated, but if you know you have a semi-integrated (short, press-in bearing cups in the headtube) and you have a 1 1/8″ (non-tapered) headtube, there aren’t that many options…

Here’s one, Ritchey are decent:
http://www.wiggle.co.uk/ritchey-comp-press-fit-semi-1-18-inch-headset/