Just to save the confusion above (from some years ago it seems) the first of the BA 737-236 fleet came in February 1980, and were pretty much all complete within 12 months. The Airtours batch, a separate order and group of registrations, were delivered in parallel, the first coming just one month after the first mainline one. There was quite an element of back/forth between the fleets, especially in winter when the Airtours utilisation was down. The second group of BA aircraft all came in winter 84-85; they were some of the last original 737s built. The mainline fleet were used by and large to replace Tridents at Heathrow, although a few operated from Gatwick as well. They were slowly sold off early this century after 20 years or more of service, when the A319s arrived.
BA were no stranger to the 737, as during the (seemingly recurrent) Trident issues in the late 1970s they leased in quite a number medium term, from Transavia and even Britannia Airways, and also into the early 1980s did several back and forth with the new Air Europe.