For future reference I managed to get them sorted...
1) remove laces
2) cut the orange cord at the 'toe' end of the sleeve on both sides and pull it through towards the heel. This may require some force.
3) Cut the orange cord as close to the stitching as possible (near the toes).
4) Thread the new cord, I had to slightly melt / harden the first 30mm of the new cord so I could thread it, you can use a lighter to do this or maybe impregnated the cord with superglue, I just carfully heated with with a jet lighter. I actually threaded 2 lengths jointed with a double fisherman knot at the toe, this should hopefully keep the cord loops even when in use.
5) Thread the new cord through each hole.
6) Feed the steel wire/rod through the sleeve (in at the heel end and out at the toe end), this was the trickiest bit and required a little patience.
7) Using a pair of needle nose pliers bend a small section of the steel wire over a bite of the cord and pull it through the sleeve. (Force was required but it worked eventually)
8) Repeat for the other side of the shoe.
9) Another tricky part... Adjusting the knot at the heel so that the cord is tensioned correctly for the lace eyelets. I did this by re-lacing the shoes and continuously adjusting the cord until it tensioned correctly. I then tied the cord off behinh the heel with a reef/square knot and a double fishermans to tidy up the loose ends. This took a few attempts to get right.
But they're now repaired for all of £5 and should take a resole as the uppers are in great condition.