Many thanks for all your replies on this one. So I'll take it that its not likely to see one these days unless Putin or similar VIP comes in on a special permit ?
Putin / Medvedev both fly IL-96-300 and in rare cases TU-204PU... and even rarely brand new Falcon 7X (they have two)
you may have a chance to see TU154 in the UK is another Atlant Soyuz charter with their TU154M VIP with some one of Russian football teams. Although, I heard that Atlant Soyuz has stopped all scheduled flights at the moment and apparently the company is going down, so I'm not sure if their VIP aircraft will be transferred to another AOC or not.
and by the way, TU154M does not need a "special permit" to fly to EU/UK. They just need to make sure there is a TU154 towbar at the airport, otherwise they will have to bring one with them.