Re: Shudokan Institute of Aikido
Just to add to what the others have said. Herts is a hot bed of Yoshinkan. Sensei Yates teaches in Watford and Hatfield [Europeanaikido.com], there is Gadi Shor a 5th dan ex hombu instructor who teaches in Rickmansworth, there is also Terry Harrison of the kenshinkai who teaches in Edgware and Borehamwood.
Having known all these instructors for many years I would recommend any of them.