Answering my own question... yes is weighted. The follwoing is copied from the moneyextra website:
"The most widely-quoted and 'popular' index for tracking the London stockmarket. For the latest index figure, click here. The FTSE 100 contains the shares of the top 100 U.K. companies ranked by market capitalisation. It's jointly sponsored by the Financial Times, the London Stock Exchange, and the Institute and Faculty of Actuaries and marketed by a company called 'FT SE International'.
The 'FTSE' is a market capitalisation-weighted index, re-weighted every day. During the day, it is calculated every minute.
Shares enter and leave the index every quarter. Additions and deletions are performed strictly in accordance with a set of rules supervised by the FT-SE Actuaries Share Indices Steering Committee, and independent body.
FTSE 100 and FTSE 250 share prices and world indices can be found in our Stockmarket section. Our Daily Business Report keeps an eye on the main business news stories - upated by 1730 each weekday. "