B&C confirmed to me 0W40 A3 B4, and that they use Mobil-1, 0W40 A3 B4 (fully synthetic). I bought a 20 litre drum of this from Opie Oils, @ just over £200, which should give me 3 oil changes.
For ref, it took exactly 6 litres to get it back to the top mark on the dipstick after sump and filter...