Grosvenor Auctions is holding a specialist sale (the first in a block of auctions) of rare Gambian stamps sourced from the collection of John F Rose, who died last year.

Rose, who travelled the world as part of his career advising oil companies collected stamps from many countries but his love of the Gambia Cameo issue inspired him to specialise in the country. A book he wrote on Gambian philately is to be published shortly.

Possibly unique: the 4d Gambian stamp sheet

Two of the highlights from the near-500 lot auction are:

Firstly, a complete mint sheet of fifteen (5 x 3) 4d brown stamps of the 1880-81 Watermark Crown CC Upright issue which is expected to sell for £4,000-5,000 (up to $8,100). This should make an excellent investment.

One of these shows a sloping value label; another has small areas of thinning on the reverse, otherwise the whole is fine and very fresh. It may be a unique sheet as only 263 sheets were invoiced, and was once the property of renowned collector Dale Lichtenstein.

The extraordinary Gambian Imperium stamp sheet

Secondly, there is an 1897 (Aug. 24) appendix sheet headed "Gambia/Colour Scheme similar to that dated January 9. 94", bearing eight imperforate 6d 'Imperium' stamps with suggested values written alongside.

The 3d has been crossed out and another 'Imperium' affixed alongside, making up the set in issued colours. Believed to be unique, this sheet is expected to fetch £5,000-7,000 ($11,300) in Grosvenor's auction which takes place in London on May 23.