WW1 Red Cross stationery cover used in 1917. Franked KGV 1d cancelled London 24 AP 17 - however T and postman's cachet, implies posted overseas, with the 1d, tax mark as underpaid and cancelled on arrival in London. 

Marked On Active Service, as such a concession was allowed so cachet charges 1.1/2d F.B. A (Foreign Branch), with no surcharge.

Collected with due stamps cancelled LONDON 24 AP 17.

(There was no formal concession for Red Cross mail, if this had been posted at a British APO free postage would however have been allowed. I think surcharged because it has been posted in a foreign postbox). 

Condition as shown: Rear flap is damaged please check pictures. 

ID: GB WW1 42174