Washing a waxed cotton jacket?

[Boffyflow]

I have a Barbour waxed utility mac which is now 3 years old and the wax coating has worn off. I'd like to machine wash it before I re-wax it, as the collar is looking a bit grubby and the jacket could do with a general freshening up.
However, it was expensive and I don't want to ruin it - but as the jacket and lining are cotton, what harm could it do?
Has anyone ever washed a wax jacket?

It is this jacket:
www.barbourbymail.co.uk/Barbour-Ladies-Utility-Mac.html

Washing instructions state 'do not wash', to sponge clean only on any dirty bits, but that won't freshen it up under the arms etc.

surely you can wash it and rewax? 'Utility Mac' that cannot be chucked into a washing machine when it gets muddy is a bit of an oxymoron doncha think!
I've washed Fjallraven wax jackets in a normal 40C cycle in a washing machine, and rewaxed using iron or hairdryer, I don't know if the Barbour system is similar?