Hi - I am always getting great tips from this forum so thought I would recommend this internet site for sending flowers in the Uk:
Flowers by post with free UK delivery | Bunches the online florist
I sent some a few of weeks ago to my Mother-in-Law and she said they were the best flowers she ever received, they lasted ages and loved the fact they included a small box of chocolates. She was that impressed she wrote to the company to tell them - something she would not normally do. They also arrived on the due date which I picked when I purchased them.