MkXVIIIA engine flywheel magneto

Does anyone know how to get a flywheel re-magnetised? Mine now has a visible but very week spark and won't start the engine even after replacement coil and condenser.
Any help gratefully received.

Brightspark magneto services?

Brightspark magneto services website says they only do the small diameter Lucas and BTH type magnetos but I'll email them.

Problem solved! here's how.
The engine has been run for several miles now but still failed to restart when hot.
it has had three ignition coils in the last few weeks, one of which purported to be new. However the core diameter of all of them was too small and had been bushed out to fit. (This is fairly common practice). The coil also had the central contact for the ht lead placed off centre by about 7mm. I returned it and was offered a rewound coil on the correct core in a few weeks time.
it arrived, was fitted and now has the best spark ever in the 54 years of owning the bike. I suspect the insulation of the various coils was breaking down when hot.
In dismantling the magneto many times whilst replacing coils I began to notice that the iron keeper bar I used to retain magnetism seemed to be increasingly attracted to the flywheel. Of course I do not have the equipment to measure and prove this but it seems so.
I read on the web a method for re-magnetising a flywheel by spinning the engine (with an electric drill). An explanation of why it works is attributed to a chap called Fred Holmwood. it seems to be working with mine, so just get it going and use it, but make doubly sure the coil is good.