The BHS bridleways book: Lincolnshire on Horseback is still available and all the rides I've tried from it have been lovely. EGB Lindum run several non-competitive rides throughout the year http://www.lindum-egb.info/
Thanks for those suggestions. I did the one on bank holiday monday at little bytham. Unfortunately my horse didnt like being on her own and I kept finding myself tagging along with various pairs of riders. I have an old copy of the bhs linclnshire rides but assumed it would be out of date by now.