Google gives three organisations who quote their banking details as Barclays Sort code 20-36-47. So it is probably a office only: 7th. Floor, United Kingdom House, 180 Oxford Street, London W1D 1EA. ......50 South Mall, London SW1Y 5AX. ........ Hanover Square Corporate Banking Group, P.O. Box 15163H, 50 Pall Mall, London SW1A 1QD. Hope this is of some help.
But sort code = branch is not a reliable indicator these days. A lot of banks use local regional offices for processing cheques from several branches, so a sort code can = several branches