Does anyone have any experience of being able to get a 3 brg diesel refurbished to reduce excessive smoking and oil consumption without having to buy a stripped engine or is this generally the best route to take. I only anticipate doing small annual mileages and would probably only need piston rings replacing, valve stem seals and a gasket set. Any advice

even the small works you have mentioned are likely to cost you circa £350 of someones time - a stripped engine would cost at least twice that

a good used engine can be picked up on ebay for less than £100 so it's only really practical to DIY unless you have won the lottery