Sorry, I missed all these messages looks like I forgot to turn notifications on again. Many thanks all for chiming in
The result for all those interested and those with ABS models wondering if the same is possible:
1. I bought the axle in the link (for those from the future it was a TDM 900 front wheel axle, listed for the ABS model but actually from a non-ABS). The difference between the two is not the axle but the spacers (non-ABS model has two). On the ABS model, the hub insert (which sits against the wheel rather than being fixed) acts as a spacer.
2. I also preempted I may have some trouble with the bike's electrical systems so I bought some new braided racing set-up brake lines to bypass the ABS pump (standard lines feed to the ABS pump on their way to the wheel). I don't know if this is necessary, but makes the bike look a bit blingier anyway and I'm hoping to dig out the ABS pump at some point and sell it.
3. The ABS warning light and engine warning light are now illuminated. I will find a fix for this at some point and update this thread as and when, but having just passed MOT I'm not fussed by it for now.
4. The speedo no longer works (frozen at zero). This was something I thought was a possibility but had hoped I wouldn't have to deal with. The TDM has its speed sensor on the output shaft on the front sprocket. I think this may well only be in use for non-abs models only. I think the ABS models will take speed from the ABS sensor on the front wheel. I think I'll look into fixing this by purchasing a used speed sensor off ebay and seeing if it is a straight wire in jobby. This is only to keep my mileage updating so I can easily update my fuel economy on fuelly. For those of you with pristine bikes that are low mileage and still worth something I would recommend holding off for a solution on this one before attempting. For me, I don't really care beyond fuel economy. I ride the same number of miles give or take per month so I do my servicing by time intervals than miles, and it won't be worth anything by the time I've killed it - which is the harsh pragmatic truth of my relationship of convenience with this terrific bike.
5. I may not bother with the speedo though as I'm looking for an excuse to install a Garmin Zumo
Given the number of you that will have just read that: two warning lights and no speedo, and think they don't want to ruin their bike or chase gremlins to try and fix it - I think it's absolutely worth it. It handled suspiciously well for the bike I thought it would be when I bought it. But now, now it's something else. I only got to play on a few roundabouts but this thing will really get about on the twisties now.
Felt a little more unstable filtering through traffic on the A2 (national speed limit dual carriageway and 50mph average speed zone) but that's to be expected given reduced gyroscopic effect. White lines seemed to affect it more when splitting in terms of unsettling the bike - I think that's more to do with it being 1/2" lower at the front than momentum of wheel. Nothing different from a Non-ABS model in those regards