Update: The adjustable spanner worked great. In fact I think because the caps were pretty loose we could have used almost anything! Paper clips, chopsticks, #2 pencils, baby teeth...

Info for others with same/similar model: My BB is slightly different from the one on velobase (see previous post). Mine is marked "Type: Track" (even though the Circuit was a road bike). Will take a photo of the label and post up later. Also, surprise surprise, these BB's use sealed cartridge bearings.

Thanks for everyone's suggestions and insight. Frame is now ready for prep and paint!