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WHAT: Extending the Royal Commonwealth Society's existing Commonwealth Club into a next door building, which was a Turkish bath in the 19th century and more recently a Barclays bank.

The project will add 10,000 sq ft of extra space on the ground, lower ground and mezzanine levels, including a 220-seat auditorium, an internet touchdown point and a new members' lounge and bar. The scheme will see the club extend from its current premises at 18 Northumberland Avenue into adjoining premises at number 25.

HOW MUCH: Final project cost was £4m

WHEN: ÐÇ¿Õ´«Ã½ started in December 2004 and finished in December 2005

CONTRACT: JCT 98

HISTORY: In the late 19th and early 20th century the Charing Cross Turkish Baths stood at 25 Northumberland Avenue. The baths took nearly three years to build and cost around £30,000.

Gentlemen entered the building through the front entrance on Northumberland Avenue to use facilities including a suite of bathrooms, while women entered by a side door to use their own smaller set of baths.

The most famous person said to have visited the baths is Sherlock Holmes, a claim made by Dr Watson in The Illustrious Client.

The baths were closed in 1948 and the building subsequently became a Barclays bank.

Meanwhile, at 18 Northumberland Avenue the Royal Commonwealth Society re-opened its doors six years ago. The club's success since then made it necessary to expand its premises.

WHO: QS, PM, contract administrator and M&E engineer: Mellersh & Harding, interior designer: MoreySmith, structural engineer: Michael Hadi Associates, fire consultant: The Menzies Partnership, contractor for enabling works and fit-out: Ibex Interiors.

PROJECT TEAM'S VIEW: "It's a great project but in terms of complexity it was a nightmare. The most difficult bit was making the shell because we had to put an auditorium in the basement, and to do that we had to remove some of the structure supporting the residential flats above. The residents were in situ so we couldn't do any of that work out of hours, which conflicted with the client's business, so that was a challenge too. But technically it was an interesting project." - Andrew Webster, equity partner, Mellersh & Harding

CLIENT'S VIEW: "To help disabled access we also needed to have a lift designed for us with doors on adjacent sides, rather than opposite sides. And we didn't have enough space to put the guts of the lift above the car so instead we put them under the lift, which is rare. It's an unusual lift, if you get excited by lifts." - Shaun Whitehouse, club manager, Commonwealth Club