None (as yet)

I have finally found the answer to where the Ricky Tick Club scene was filmed!
I have recently been in touch with Paul Welsh, who is the Elstree Studios official historian and he had this to say about the matter in response to my enquiries on 20 March 2013:
ME: Do you know where the Ricky Tick Club scene from Blowup was filmed? On a set or location?

PW: I interviewed Roy Parkinson who worked as an Assistant Director and Production Manager on 21 films made at MGM over the years. He worked on Blowup and said it was nearly all location shooting except for a club scene that was to have been filmed in Windsor but was delayed. Filming stopped for a couple of weeks while the director assembled a rough cut of the film. When they restarted it was decided to shoot the club scene at the MGM studio.


ME: Was any film actually shot in/used from Windsor itself, do you know?


PW: No. Roy never said which sound stage was used. He mentioned various London sites but none in Windsor. He thought they filmed the scene at MGM as a particular singer or somebody was not available for the original filming date but he was recalling this over 30 years later and sadly is no longer with us.


ME: Did he have anything else of note to say about the filming?


PW: Roy also said that Antonioni turned up at MGM with a script of just 76 pages which made it very hard for Roy to breakdown a schedule for filming. Roy would look at a scene and say for instance that's half a day to film but Antonioni would just turn round and say 'I might spend 3 days shooting it but I have not yet decided.'


He also said David Hemmings would turn up on set worse for wear being a new young star in the 60s who enjoyed partying!


Based on this discussion I will consider the mystery solved. Now to find out which sound stage was used, and its present location as, sadly, MGM British Studios have long gone...

This is the scene at a Ricky Tick Club where David Hemmings:
Enters the club seeking Vanessa Redgrave;
'Strolls on' through a Yardbirds gig;
Passes the dancing figure of Janet Street-Porter;
And leaves with just the neck of Jeff Beck's broken guitar.

Investigations confirm that this was shot at Elstree Studios in Borehamwood, where Antonioni had a set built that was an authentic replica of the Ricky Tick Club at Clewer Mead in Windsor.

Sadly, Clewer Mead was abandoned around the time of the film, and has since been demolished. It was located roughly where the present-day Windsor Leisure Centre now stands (see images below).

©1967 John Handcock. 
25_001. Clewer Mead in its abandoned state (i
mage supplied by Roger at Thamesweb).

©2010 Google Maps

©2010 Bing Maps
25_003. The site from above.