I decided I would try grafting on two different varieties - Egremont Russet and Merton Russet. I don't have any other russet varieties so thought I would give them a try. Egremont Russet is one of the varieties recommended in Martin Crawford's Creating a Forest Garden. It ripens in October and stores until December and has some resistance to scab. Merton Russet is a later apple, ready to eat between December and March. I bought 9 scions of one and 6 of the other from Deacon's nursery. These arrived a couple of months ago and have been kept in the fridge since then. I also planted a couple of trees at my kids school recently. I pruned them after planting and kept the prunings as well, so I had a single scion of both Katy and Scrumptious (both earlies).
The only tools I used were: a sharp Opinel folding knife, Tenax grafting wax from the garden centre and Parafilm tape from ART. Having cut each branch off and tidied up the end I made a small cut (~2cm long) through to the cambium layer and eased the bark away from the inner wood. Then I cut the scion from both sides at a shallow angle to make a sharp end and slid this under the flap created in the branch (see here for a demonstration). Once I had done two of these I applied the warmed wax to seal all the open edges and wrapped it in the tape. Lastly I put some labels made from a cut up ice-cream tub on the branches so that I know which are which. I left about one third of the original branches to draw the sap. I may leave them in place if the nematodes I used last year have got rid of most of the codling moths.
I'm not sure if I did it right, but the process was fun and I'd recommend trying it out. Hopefully at least some of the grafts will take. If they all do I'll have a tree with five varieties in total that will provide apples from August through to March.