If you want to convert those 1978 figures to more recent ones, there would be a choice of indices depending on how you word the question to be answered. The first choice would be a GDP deflator (what used to be called the implied index of total home costs). This is the index that converts to a notional inflation-proof money, using which the GDP increase in volume terms matches the increase in money terms.
This does not tell you what today's price would be - no index can, and anyway the same items could not be made or bought now. It should take out inflation in the sense of how money changes its value, averaged over the whole economy, not just over retail spending. Subject, of course, to the difficulties of estimating GDP in volume terms.
Anyway, the factor from 1978-9 to 2012-13 is 24.279. (Source
www.gov.uk/statistics.)