Ill give them a bell and put on my best phone voiceis there no club discount? I'm also a member of Mk2 Golf Owners Club. They have a deal with Heritage that paid members get 5% off. Membership is £7 a year.
That would get you £22.50 off, but of course you'd have to pay the £7 so you'd only save £15.50 but it's better than nothing. It's not code based, once you're a member call them and they'll apply the discount to your account so from then on as long as you're logged in you'll always see the discounted price.
Heritage do have 10% over £100 quite often with Easter fast approaching it's quite likely they'll have an offer soon. make sure you sign up for their newsletters. Or just call them and see what they'll do for you. In my experience they've been pretty good over the phone.