You could try, putting a bead of clear silicone as high up as possible, then fit a length of 225mm dpc along the wall, lapped down over the lintol and to outer brickwork edge.
Leave a few weep holes in the perps, on first course over lintol.
Grt idea...but...Stuart45 is right on the money...first course in...now the tricky bit...
I may be able to lap the old DPC...iv'e freed it up a little by chipping out some obstructive mortar...
fingers crossed...and thank you both for your continued input, its appreciated...