That would really be very usefull in assessing the performance of a portfolio.
Yahoo has you covered. Go to finance.yahoo.com, click on symbol lookup, and the search for name FTSE with settings type=indexes and market=worldwide. (The major indices in the UK are generally all published by FTSE.)
For instance, for the FTSE 100, you have http://finance.yahoo.com/q?s=%5EFTSE (ticker is ^ftse). Click on historical prices over on the left, then set your date ranges. You can then download the data with the 'download to spreadsheet' link at the bottom.
Make sure to use the adjusted closes to calculate returns to compare your portfolio against (which account for dividends and splits!)
Here is a list of major indices:
FTSE 100
FTSE 250
FTSE 350
FTSE Smallcap
FTSE All-Share
FTSE techMark 100
FTSE AIM All Share Index
Hope this helps!