UPDATE 1-Galliford, Costain JV gets 400 mln stg deal extension

* Say JV with WS Atkins gets contract extension

* Contract is from United Utilities

* Costain's share of contract is worth 180 mln stg

* Contract to commence from April 2010 (Adds details)

July 6 (Reuters) - British construction firms Costain Group Plc and Galliford Try Plc (GFRD.L) said their joint venture with engineering consultancy WS Atkins Plc (ATKW.L) had received a five-year, 400 million pounds ($651.2 million) contract extension.

The asset management programme-5 contract with United Utilities Group (UU.L) commences on April 1, 2010 and Costain's share of it would be about 180 million pounds, Costain said in a statement on Monday.

Separately, Galliford Try said the contract covers capital works in the North West of England, and will consist primarily of improvements to water processing plants.

The original contract started in 2005 for implementing United Utilities' non-infrastructure capital delivery works programme in its southern area.

At 0750 GMT, Costain shares were up 2 percent at 25 pence, Atkins shares were down 1.6 percent at 575.5 pence, while United Utilities shares were down 1 percent at 485.5 pence on the London Stock Exchange. Galliford shares closed on Friday at 47 pence. ($1=.6142 Pound) (Reporting by Usman Merchant in Bangalore; Editing by Gopakumar Warrier)