Update: I have clarified the status of this bird with the Secretary of the BBRC: it is considered to be the same individual first seen in Somerset on 5th January 1986 and then again there in subsequent winters until 3rd March 1990. Thus it is considered the second sighting of the first record for Britain. The BBRC Secretary indicated that the photos taken at Ibsley Meadows were likely the only time it was photographed.
This photograph was taken by Louis Rumis at Ibsley Meadows near Ringwood, Hants, UK in late January 1987. It shows a Tundra Swan Cygnus columbianus columbianus with Bewick's Swans Cygnus columbianus bewicki that I had found a few days earlier - I believe this was the first accepted record of Tundra Swan for Britain (but not Ireland). Even when in a larger group of Bewick's, this bird looked larger and taller-necked; the yellow facial teardrop was c.7 - 9 % of the bill profile (my estimate), and very dull in tone. For USA birders, note the bill pattern of the adult Bewick's feeding in the center, and compare it to the left/rear bird on the cover of BIRDING Vol. 26 No. 5 (Oct 1994) - a bird apparently photographed "somewhere in North America" - that looks like it is a Bewick's. For British birders, compare this bird to photos of other individuals in Great Britain since this date:
The image below is from Evans and Sladen: "A COMPARATIVE ANALYSIS OF THE BILL MARKINGS OF WHISTLING AND BEWICK'S SWANS AND OUT-OF-RANGE OCCURRENCES OF THE TWO TAXA" The Auk, Volume 97 Issue 4, 697-703.