Thanks didn't realise it was that simple! And it's only now that you point out what your avatar is that I can see it's a cat. How did I not realise that before?
Charles Stanley are another good (and cheap) brocker. Just set up account and invest in something like the 'Vanguard US Equity Index Fund Acc'. If your really quick, you'll be able to use this year's ISA allowance
This could be as simple at opening a nutmeg account.
The real challenge with trackers is finding the cheapest.
Also, don't take advice from an upside down cat on a bike forum - he might not be an IFA :)