Street scenes set in both London and the USA have an old British "Bristol VRT" double-deck bus, painted in London bus red. This type of bus was never used in London, and they were out of service elsewhere in the country well before the setting of the film. The same vehicle appears throughout the film.
After the skiing photo-shoot, a fictional English newspaper (the cover price is in Pounds Sterling) bears the headline 'Missing boy found in car trunk' rather than the correct 'found in car BOOT', as would be used in the UK.
At one point, their University is referred to as "St. Andrews College". St. Andrews is not a college but a University which consists of two colleges St. Mary's (for theology only) and The United College of St. Salvators and St. Leonards (for every other subject). There is no such place as "St. Andrews College".
The Aircraft and Helicopters used all had American N registrations. The Aircraft would have been Queen's Flight RAF and would have borne registrations in the Zxnnn range, the helicopters would have had similar range, Neither were types which are used by the RAF.