You seem to miss the point. It is not a question of whether or not the films are good. Good, bad or indifferent, they would be received in the same manner. Eg. Name me one film financed by the British establishment (UKFC, BBC, Film Four) that premiered at a major festival in the past ten years and received a one or two-star review from a mainstream British journalist.
Now that's just begging for someone with more time than me to do some checking...
However, it's certainly NOT my experience - I have never been struck by the gushing reviews of British films by British critics. Indeed, some of the worst reviews of any films over the past few years have been British (OK - so I know Nothing isn't referring to films such as Sex Lives of the Potato Men or Lesbian Vampire Killers, but still). Even sticking to more attractive art-house fare (Loach, Leigh, Arnold etc.), the tone is often more 'not bad, but nothing new' than 'WOW!' This could well be because (arguably) the default mode of British 'Serious' Cinema is realist, and these directors largely fall within that tradition. Now this doesn't mean there is not a huge difference between Loach and Leigh in many substantial areas, but their films fall broadly within the realist' tradition.
So a new British art-house film is readily understood by mainstream critics as falling within the tradition of quality filmmaking - at least that branch that does not include corsets and frills. Therefore, there may well be a pre-disposed cultural preference for this mode of filmmaking - as well as the 'well it's good, but nothing we haven't seen before' (cf many of the reviews for Leigh's All or Nothing
) - which is not really the same as a cabal of critics planning their reviews in order to con art house audiences to see the latest British film. As an aside, I remember when Barry Norman chose Distant Voices, Still Lives
as one of his favourite films of its year, it was with the proviso that he respected it as an important film and admired the skill with which it was made - but didn't actually like it very much.
As a final thought - who remembers Splitting Heirs
? An Eric Idle "comedy" actually selected for the Cannes main competition in the 90s. Not in the 'realist' tradition, and not a costume drama (it owes more to Ealing and Kind Hearts in particular) - and not very good (to put it mildly). Slated by the critics and disappeared at the box office.