Small Business Valuation Firms in the UK

Does anybody have any experience or contacts/recommendations for firms that can do small business valuations in the UK? A contact of mine has asked me, and my first thought would be a reputable accounting firm. However, I was wondering whether there are specialist valuation outfits that do that kind of work, whether in the UK or elsewhere. The company in mind is small, sub £500k in annual revenues and registered in the UK so will have abbreviated accounts publicly available.  Any suggestions or recommendations would be greatly appreciated.