Joe Allen's magic will continue despite Robert De Niro's plans

Perhaps it's not so hard to believe that Joe Allen, the West End restaurant beloved by theatre-goers, is 40 years old after all. It's a much loved part of the London theatrical landscape; this was made abundantly clear by the social media outcry last November when it was revealed that Joe's would have to vacate its present Exeter Street location, owing to Robert De Niro buying the entire block and redeveloping it as a boutique hotel. De Niro was not in attendance at the 40th birthday party, which was probably just as well given the loud boos that rang out every time his name was mentioned. Who knows, maybe he would have ended up wearing one of Joe's "secret burgers" (the burger is always available but it isn't on the menu).

Reading the visitors book at last night's party, it is also clear that so much of London's showbiz community considers this dark-wooded, brick-walled, dimly-lit haven, the walls a treasure trove of theatrical posters, a home-from-home. For years the exterior was marked only by a discreet brass plaque (a canopy and overhead sign have since been added) so entering always made you feel like you were somehow "in the know".

Plans are to sell off pieces of the central brick wall as souvenirs, a bit like the Berlin wall

Joe Allen opened his first restaurant in the basement of a New York brownstone in 1965 essentially as a reasonably priced, late-night canteen for Broadway actors craving a meal and hangout after their curtains had come down. The stars flocked to it and it's still there today (Allen himself still lives in the building "above the shop"). The London version opened in 1977, apparently partly in response to the American cast of A Chorus Line, then newly opened at Drury Lane, complaining that everything was closed when they finished their show every night. There's a Paris Joe Allen too, also still going strong.

At last night's party, held in support of the theatre education charity Mousetrap Theatre Projects, owners Tim Healy and Lawrence Hartley announced that they are in talks to move the entire gaffe ("the walls, the floors, the bar, everything that you love") to a new Covent Garden venue this summer. Cathy Winn, the general manager whose glorious brand of camp charisma is at the very heart of Joe's, wants to sell off pieces of the central brick wall as souvenirs ("a bit like the Berlin wall, darling") which could take care of Christmas presents for the theatrically minded this year.

Robert DeNiro wasn't there, but it was probably just as well

As befits what really is a theatrical institution, there was terrific live entertainment last night, hosted by London's 'Night Tzar' Amy Lamé, from a host of Joe Allen regulars including Scarlett Strallen, Tracie Bennett, Sheila Ferguson, Peter Straker, Miss Hope Springs, Harriet Thorpe – who actually waitressed here when it first opened- and Jay Rayner who credits Joe's as "the place that taught me how to eat", which is a pretty big compliment given that he is now one of the capital's most respected food critics.

One figure absent from the celebrations but very much there in spirit was Jimmy Hardwick, the adored pianist and West End legend who had played every night – barring holidays – since Joe Allen opened through to his death in 2012. Jimmy's special skill, aside from making guests feel incredibly welcome, was in playing a snatch of music pertinent to whichever theatrical luminaries had just entered the room. This occasionally became rather bewildering around the 11pm mark when stars of numerous West End musicals tended to arrive en masse, with Jimmy performing impromptu mash-ups of everything from Lloyd Webber to Sondheim and Porter. These medleys were even more outrageous if Jimmy had just been topped up with house white. He was a one-off, and his star-studded, wonderfully flamboyant memorial service at St Paul's Church was one of the theatrical events of 2012. The piano playing baton has now been passed on to Jilly Bean who is similarly in tune with the adorably eccentric Joe Allen vibe.

I even celebrated my own 40th birthday twice at Joe Allen

I've been regularly visiting Joe's since I was 15 years old (my aunt's best friend was dating Harry Chambers, the maître d' at the time) and can map events of my life – from heartbreak to celebration and back again – by which table I was sitting at on any given occasion. I even celebrated my own 40th birthday twice at Joe Allen, firstly on the day itself in NYC and then a week later at the London branch.

This place is more than just a restaurant. It's an institution, and it will be fascinating to watch what happens as Joe Allen moves to a new location while still hopefully preserving the magic and heart that makes it so special. I fully intend to be there for the 80th birthday party. Mine's a margarita thanks, straight up and with a salted rim. Happy 40th, Joe Allen.