Thames Water used Finsbury in a bidding war that saw Kemble Water - a consortium led by Macquarie's European Infrastructure Funds - prise the company from German owner RWE.
The agency, which advised on 13 M&A deals overall in October, also worked on Royal Dutch Shell's acquisition of the final parts of Shell Canada for £3.4bn.
Aura Financial entered the top ten in second spot due to its work on Xstrata's £9bn hostile bid to boost its share-holding in Canadian miner Falconbridge, from 19.9 per cent to 100 per cent.
The Xstrata bid saw Aura push ahead of Financial Dynamics, in third after 29 deals in the month - by far the biggest of which being its work on Indian firm Tata Steel's £5.1bn bid for Corus.
Brunswick sat on the other side of the steel deal, propelling the agency to fourth.
Tulchan came fifth, aided by advising Electric Invest Acquisitions' £2bn buyout of Northern Irish utility company Viridian Group. Maitland advised the latter company, raising the agency to eighth, behind Cardew Group (sixth) and Vaishnavi Corporate Communications (seventh).
Citigate Dewe Rogerson and K Capital Source worked on nine and two deals respectively.
SEPERATELY... Smithfield was also involved in one of the month's biggest deals, advising Macquarie on its involvement in the £8bn sale of Thames Water.
DEAL WATCH October 2006 ranking
01. Finsbury - 13 (No. of Deals) - 16,784 (Deal Value £m)
02. Aura Financial - 2 - 11,995
03. Financial Dynamics - 29 - 9,827
04. Brunswick Group - 17 - 8,349
05. Tulchan Communications - 6 - 4,989
06. Cardew Group - 6 - 4,526
07. Vaishnavi Corporate Communications - 1 - 4,300
08. Maitland - 6 - 2,713
09. Citigate Dewe Rogerson - 9 - 2,667
10. K Capital Source - 2 - 2,060
Source: Zephyr published by Bureau van Dijk