Gold Britannias were first issued in 1987. Four coin Britannia proof sets have been issued every year since 1987, switching to a 5 coin set from 2013 onwards.
Live Metal Prices
If you know the actual gold weight of the product you are buying, you can calculate the intrinsic price from the live gold price. If you wish to know the intrinsic value when you bought the set you can follow this link to historical gold prices. We have a blog on spot price and premiums which may be of interest to you.