You've a couple of options Keith:
1. Check out a scrap yard (see Services page for links), the same 1kW starter motor also appears on the '95 Mirage.
2. Camskill - be prepared to fork out a few quid, send your old one back and then get a refund.
3. Get the car down to a decent auto-electrician, there are clutches, brushes and armatures that may be servicable.
4. Get under the engine (LHS) and give the starter a smack of a hammer (yes, really!). This might free up whatever is making it stick. Try it first, you might be surprised. See pic below (ref 16-010) if you're unsure of its location.
CJ