Tuts,
As you don't have a full aircrew medical we've got to very strongly recommend you bite the bullet and go for the civilian Class One medical. It can only be undertaken at the main CAA centre.
Yes, you can do the PPL without it but a consequent failure of class one would halt going any further. No matter how fit you are please take this advice seriously. Our private correspondence sadly shows a long history of extremely keen but ultimately disappointed people.
The £400 is but a gnat bite in comparison to what you're planning to spend.
Regards from the Towers
Rob