TBH I don't think you'll get a 'good' Nikon for £25 or under - I would just stick with your OM-10 which is a great camera. Nikon's entry-level cameras (F50, F60, FM10, F-401/601) are a bit pants (severely lacking in features), and their decent cameras (F-801, F3) are rather more expensive.
I would recommend an F-801 or an F90, both are about £50 on ebay, but you could probably find either for £10-20 at a car boot sale or jumble if you're eagle-eyed.
TBH I don't think you'll get a 'good' Nikon for £25 or under - I would just stick with your OM-10 which is a great camera. Nikon's entry-level cameras (F50, F60, FM10, F-401/601) are a bit pants (severely lacking in features), and their decent cameras (F-801, F3) are rather more expensive.
I would recommend an F-801 or an F90, both are about £50 on ebay, but you could probably find either for £10-20 at a car boot sale or jumble if you're eagle-eyed.