Under the Consumer Sales Act you have certain entitlements. If a company goes beyond that that is their option. As far as I am aware Rega Lifetime Warranty covers manufacturing defects, which you would have to prove.
In the event of a defect under UK law:
- First 30 days you are entitled to a refund
- First 6 months the company can repair or replace unless the company can prove the problem is of your making. If that fails to solve the problem the you are entitled to a refund.
- After 6 months you would have to prove a defect and you may have to go to small claims court. You may not get full value compensation/refund. You have 6 years to make the claim (5 in Scotland).
I would not expect my decades old Planar 3 to be repaired under warranty. Any manufacturing defect would have shown up by now. Any failure now would most likely be wear and tear which would not be covered. While it is not impossible for a manufacturing defect to show up years later (washing machines and tumble driers, spring to mind) but I would think it fairly unlikely.
If you are concerned, I'd speak to a dealer. Rega Service Centre require you to go through an authorised dealer, so they would know how easy it is to work with the company and what their warranties actually cover. They'd should also have a good idea how reliable the equipment is, in general.