If you can get one, check out Goldring's GR2 P2 clone - RB250 arm, Goldring 1012GX cartridge - £165 from £270. Leaves you £335 to get the rest - £100 on the Tannoy's, £200 on the Marantz. You'll get a higher end arm, a far better cartridge (individually, they go for around £120 each respectively) and better performance.
Alternatively.....get a secondhand Technics SL1200 for about £250, Cambridge A340 amp, P540 or 640 phono amp and the Tannoys. When funds allow (as you will go over the budget a little) get a better cartridge, upgrade the mat on the Technics and you have a deck with superb build and the prospect of improving further over time - you could have a seriously good deck if you get the arm upgraded. Might not be what your boy wants, but as a project, it beats the Pro-Ject in the end!
(Sorry, couldn't resist that one!)