Thanks for the extra info/advice......Found a Landy welder in Bolton. He has done dozens of them and wont remove the bulkhead to do it or the floors. He is happy for me to order the outriggers from Paddocks. He reckons its a fairly straight forward job if the rot has not gone back as far as the main chassis.
Booked in for next Tuesday so will hopefully share some tips on short cuts with you, pics etc. £60 for a pair of outriggers inc P + P from Paddocks. May as well go for the 'propper job' rather than patching. Re test 2 days later. Will update
Anyone needing an MOT?.... Nationwide Auto Centres are doing a half price test for £27 if you book online.

how much for the labour out of interest?

Update.....I have had the new front outriggers fitted. I supplied them (£60) and it cost me £125 to have the old rotted ones removed and the new ones fitted. The old ones had been repaired before. One patch was so thin you could bend it with your fingers.
Passed the MOT no probs and the guy who tested it was a Landy owner and we got chatting. He says he double checked the welds and they are complete and solid. So I am happy with the job.... £185 total.
I think it was a good decision to replace rather than patch up and I did the same with my rear crossmember a month earlier (£350 fitted)
£535 spent on getting the chassis good for at least 5 years.... thats getting on half the price of a new galvanised chassis (Ex VAT and fitting) so I can see the merit in replacing..... maybe next time I think when I come to sell her, new outriggers and crossmember should be a stronger selling point rather than patches.

Pics of before and after.....