The record for the fastest unsupported row around the British mainland by a team is 26 days 21 hr 14 min and was set by Lt William de Laszlo, Lt Ben Jesty, Sgt James Bastin and William Turnage (all UK) who departed from Tower Bridge, London on 7 June, rowed clockwise around the mainland and crossed the finishing line back at Tower Bridge, London, UK on 4 July 2005.

The row was physically unsupported but they did have radio contact with a shore based team.
They rowed in a 24 ft boat which had been designed to hold sleeping quarters in one end and essential supplies in the other.
They rowed in pairs in two hour shifts.
Full details can be found on http://www.gbrowchallenge.com
De Laszlo, Jesty and Bastin are Grenadier Guardsmen.