I should add that it's the pedal thread that's been completely stripped within the crank arm.
I've given my XTR crank to a local re-boring company.
Am I correct in thinking it's a 9/16th and 20 pitch that I / they need? If so I might need someone else to do the job.

Do you know anyone who does this?
No LBS I have called has even contemplated it.
If not, where can I get the tap and a correct helicoil?

Pearce cycles would do it for you, post it to them fixed and post back. They're an engineering place as well so know what they're doing. And some of the nicest people around too.

Thanks Steve.
You're right, nice guys.
They're looking at what the pitch is as my local guy can do it, but desn't have anything for a 20 pitch & have taken my contact number.
If this is the case, I'll retrieve the crank send it up to them.

9/16" x 20tpi (threads per inch)
Weldtite do what they call crank bushes and taps
http://www.weldtite.co.uk/pdf/weldtite_cyclo_tools.pdf

also Cyclus
http://www.cyclus-tools.eu/tretkurbeln.html?&L=3

http://www.vartools.com/catalogue_var.pdf
Kit de réparation des manivelles
Permet de faire un nouveau taraudage à une cote supérieure
(5/8’’x24 tpi) dans les manivelles recevant les axes de pédales
et donc de conserver vos manivelles.
Enduire l’extérieur de la bague réductrice de frein-filet
NL-77400 puis la visser dans le taraudage.
Enfin, replacer l’axe de pédale dans la bague taraudée.
Les tarauds s’adaptent sur le tourne à gauche DV-04330
Ce kit comprend :
– 1 jeu de 2 tarauds-aléseurs (D&G) 5/8’’x24 tpi
– 5 bagues taraudées pour manivelles droites
– 5 bagues taraudées pour manivelles gauches
– livré dans boîte compartimentée
PE-04703-5 – sachet 5 bagues 9/16’’x20 tpi coté droit (jaune)
PE-04704-5 – sachet 5 bagues 9/16’’x20 tpi coté gauche (grise)
A utiliser impérativement avec l'huile de coupe CD-77000-00250