D&R has the Leupold Vari-X II 6-18*40 AO with target dot in Silver for $374 (may be on closeout though). May squeeze in under your budget after shipping, duty, vat and coversion to £?
http://www.dnrsports.net/miva/mercha..._Code=LEU49635
other than that most silver scopes seem to be 3-9 or 4-12 mag or thereabouts from Bushnell, Swift etc.
Edited to add, Weaver Grand Slam 6-20X40 in black and silver is $375 from Straightshooters:
http://straightshooters.com/weaver/wgslam62040.html
again may squeeze through the budget constraints on import.