Who are the top 10 largest online brokers in the UK and how clients does each have?

Greetings Tradermind-ga, 

I assume that since you didn’t mention a specific kind of broker, you
mean stockbrokers.

This looks like the best top 10 list of online Brokers in the UK over
the last two months, according to www.find.co.uk, the leading Internet
directory for UK financial websites.
http://www.find.co.uk/financial/Top_10s_on_FIND/Top_10_Online_Brokers/

I’ll list these top companies and their web addresses:
1. Deal4free.com - http://www.uk.cmcplc.com/spreadbet/index.asp
2. The Share Centre - http://www.share.com/
3. Alliance and Leicester  - http://shareinfo.alliance-leicester.co.uk
4. iDealing.com - http://www.idealing.com/
5. E*Trade UK - https://uk.etrade.com/splash.cgi?jump=adb_a
6. Halifax Share Dealing  -
http://www.halifax.co.uk/sharedealing/home.shtml
7. Hargreaves Landsdown Stockbrokers  - http://www.h-l.co.uk/
8. Hoodless, Brennan and Partners -
https://www.hoodlessbrennan.com/indexoffer.htm
9. City Index - http://www.cityindex.co.uk/index.cfm
10. Charles Schwab - http://www.schwab-worldwide.com/Europe/

Sorry I was not able to find client number information since that was
very hard to find. Should I be able to find this information, I will
post it as a clarification.

Here are other lists in case you need more information:

Here’s an A-Z Stock Broker List for the United Kingdom
http://www.a-z-stock-brokers.co.uk/

Here’s another list of online stock brokers in the United Kingdom
though with no rank.
Financial Supermarket.com and Financial Center - Online Stock Brokers
UK
http://www.stocksplayers.com/unitedkingdom/so.html

Cheapest Share Dealing UK stock brokers list
http://www.cheapest-share-dealing.co.uk/stock-brokers.shtml

Search strategy on Google:
top united kingdom stock broker
top united kingdom stock brokerage
top united kingdom online stock brokers
top 10 british/uk stock brokers online

I hope this has provided you most of what you need.

Techtor-ga

These links could be useful for geting closer to the answer:

E-TraderUK
http://www.e-traderuk.com/stock.html

UK Internet Share Dealing Report 2000
http://216.239.51.100/search?q=cache:lDKDmGwoJKAC:www.leeds.ac.uk/iibfs/news/execrep/ExecRpt40.pdf+schwab+barclays+turnover+million+%22uk+market%22&hl=en&ie=UTF-8