Growingpains

I work for a small architects' practice and we get referrals from builders, estate agents, former clients etc. As a thank you (and encouragement to keep recommending us) it'd be nice to give a gift to the referrer. Nothing huge - ideally a bottle of fizz, nice meal kit etc something around the £25-50 mark. Does anyone have any information on how this would work from an expense point of view? I tried googling and some advice says to treat as entertainment but that's more in relation to gifts directly given to customers (rather than referrers, who are in effect providing a marketing service). Thank you