How about a small bag of mini malteaser xmas trees? Otherwise nut free chocolate I buy for my very allergic ds include minstrels, Cadbury crunchies, twirls and buttons. He can have most galaxy bars but worth checking some of the 'fancier' ones. John Lewis and wilko have nut free chocolate coins. If anyone knows where I could buy a nut free chocolate santa I'd be thrilled, ds is 11 and has always wanted to try one!
DS1 (now 13) is allergic to peanuts and all tree nuts (but not dairy). I get chocolate for him from Nut Free Chocolate People (sorry, can't link but it's easily found on Google). It's run by someone whose own DCs have nut allergies. Wide range, chocolate arrives very well-packed and I've had some excellent customer service eg. owner remembered from an earlier email that my son was allergic to coconut and offered to change the chocolates in a tin of mixed filled chocolates to replace caramels containing coconut oil with another filling (I think they've since stopped using coconut oil completely). Only snag might be how soon you need the choc because they mainly make to order so it can take a week or so to reach you, but check the website or email for current delivery times. I have no connection to the company btw, unless you count that if they go out of business, I'll lose the only reliable source of chocolate that my son can safely eat!
Sorry, just noticed that this thread started in early December. The OP has probably found what she needed from the other suggestions. I didn't know about Tesco free from truffles, so thanks for that info - I'll check them out.