Regional Pressure Settings (RPS) are the lowest forecast pressure for geographical areas across the UK and may be used for checking terrain clearance. As such they are something if an anachronism dating from times when many aircraft operated without radio, or internet access, and travelled significant distances. The effectiveness of RPS may be judged by the number of high ground wrecks that scattered this country.
Despite what it may say in some documents, RPS are not a QNH, which is the sea level barometric pressure for a specified location at a specified time and, in these information overloaded times, can be readily obtained from ATIS, ATC and online sources through such amazing technologies as Sky Demon, iPhone and Android apps and so on.
Anyone planning to operate in the vicinity of any form of Controlled AirSpace (CAS) where the base is defined as an altitude would be well advised to use the QNH of the nearest or most appropriate airfield. A look at the relevant chart will provide clues. e.g. Daventry CTA around Stoke on Trent; base 4,500ft use Manchester QNH, Manchester Low Level Route; the clue is in the name, but as the QNH at Manchester and Liverpool are usually the same use Manchester QNH, London TMA around Chelmsford; base to north 2,500ft, to south west 3,500ft use either Stansted or London QNH
As a former controller I always hated having to file reports on airspace infringement which were in the vertical plane, however, so many of those were caused by people operating on an RPS believing that they were remaining below CAS.
My own view is that the use of RPS is unnecessary and the sooner we all operate on QNH and plan carefully, the better.