At last today I was ready. My back was not playing up and the sun was shining hotly!
Jacked the car up on the four corners and cleaned the springs, brake pipes, and a few bits of chassis needing just a little attention.
Did what you all recommended; washed parts down with parrafin, after wire brushing as required. Brushed liberally Kurust, then spay painted with Hammerite black paint. Sprayed copious amounts of Supertrol into every hole into the chassis I could find were it was vulnerable. Couldn't remove the sills as DG recommended as mud flaps, fitted by Vx, rather got in the way, and as the whole inner sill areas on both sides, looking from the centre of the car, were very good, without holes and absolutely no sign of rust, I decided to leave well alone. However, knowing what you have all said about what could be under the sill covers, I sprayed a whole 250ml can of Supertrol up into the gaps between the covers and chassis, all along on both sides with satisfying drips of the stuff coming out after a few seconds.
All done and looking good. However, the MOT tester who posted the advisories I think was being very strict, although as they know this car well, doing me a favour. The springs and pipes only had a very light dusting of 'muck', which when washed off with paraffin quickly revealed, in the case of all four springs around the car (only the front two were advised on), pure black plastic coated metal, which I still treated with Kurust and the Hammerite paint for good measure, as only in two small areas was there a break in the finish, showing a very small amount of rust cover which disappeared with wire brushing.
It has been a year since I was last under the car (do not like it as much as I once did due to age!!), but I was delighted in the overall condition of the chassis and all parts there under! It did not reflect a car of 16 years age with 77,000 miles on the clock. When I think back to my first car, a 10 year old Austin Farina bodied A40, the difference is fantastic! That 10 year old car had bits of chassis missing, the passenger seat 'floated' in mid air, the sills were shot and not connected to the bodywork by anything but old newspapers, and the bodywork had rust holes the size of fists everywhere - although it still passed two MOT's in 1971 and 1972!!
The Omega is so clean on top and underneath, albeit with the infamous rear wheel arch rusting starting to show which I keep on top of regularly, pending hopefully professional attention one day of £1,000 worth! But apart from that, all is good!
Thanks for all the great advise I received from you all. Mechanical stuff is fine with me, but anything to do with bodywork and finish generally is not my speciality by any means!