No, but I did once do the trip at reasonable cost, if slowly, by Brittany Ferries (Plymouth) to Santander and then express coach to Santiago. I found the coach details in Cooks Continental train timetable. You can go a long way round by train in Spain, but the coach was convenient and our Fangio driver made superb time! Would take about 2.1/2 days I seem to remember.
I checked this when we sailed there, though haven't actually used the service.
Iberia Airlines do several flights daily to Santiago. Booked on the Internet, you should be able to get a return ticket from Heathrow for about £140. However, I think there is only one direct flight weekly to and from Heathrow (Fridays?), taking about 2 hrs. Otherwise its change at Barcelona or Madrid, taking twice as long.
these are a private airline, like sort of spain's easyjet i think. Vair nice from madrid which we used, and there is a service to santiago from somewhere, tho dunno if direct to UK, not used it. Unfortunately their website is rather pathetic, and only in spanish it seems...
There is a daily flight from Heathrow to Santiago de Compostela, operated by Iberia. In my experience this flight is usually full, which means booking quite far in advance. Other possibilities would be flying by a low-budget airline from the United Kingdom to Madrid, Barcelona and from there using Iberia, Spanair or AirEuropa. Iberia also flies from Madrid and Barcelona to Coruna. The airport closest to Santiago with low-budget flights is Oporto. I know Air Berlin flies from Germany to Oporto and I assume one of the other companies will fly from England to Oporto. There is a train-connection from Oporto to Vigo a couple of times per day. From Vigo exists a frequent service to Santiago and La Coruna.
Ryan Air probably flies to Valladolid, which is appr. 400 km from La Coruna, mainly on freeways.
La Coruna is a much bigger town than Santiago and the road-connections from there to Madrid are much better than to Santiago. The train from Madrid to Coruna passes Santiago and stops there. The bus services from Madrid to Coruna are excelent, but it is 600 km and takes its time. The fastest is the luxury-service, with three seats, one single and one double, per row, which stops only one or two times on the way.