I can't help you directly but, if the UK CAA complies with ICAO Annex 4 then the magnetic declination shouldn't be more than 5 years old. The 5-year cycle is based on years that are divisible by 5, so, e.g. ... 1980, 1985, 1990, 1995, 2000, 2005, etc. There's a caveat or two on the 5-yr cycle, but that is the basis of the whole thing.