Patent protection does not last for ever. It lasts for 20 years so it would now be out of time but I’m sorry to say that as you did not patent it at the time, you cannot go back to everybody retrospectively holding your hand out.
They may have registered the patent themselves indeed.
They may have breached your unregistered design right which doesn’t actually need registration but the time limit to pursue that under the Limitation Act is 6 years from the breach.
Even if you were within that 6 years, I can tell you now that an action like this is not going to cost thousands of pounds or even tens of thousands of pounds but potentially hundreds of thousands of pounds if not millions.
It’s unlikely you would get a solicitor to deal with it no win no fee even if it is within time, which it isn’t. I’m sorry, I know it’s not the answer you wanted.
It is such a great shame that you did not patent the idea 30 years ago because you would have had 20 years worth of royalties.
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Hopefully, I have answered your query in a way that is simple and easy to understand.
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I am happy to answer any specific points arising from this.
Please be aware that my answer is based strictly upon the information you have given me.
If you still need any points clarifying, I will be happy to reply because the thread does not close. In fact, it remains open indefinitely.
I am always happy to answer any further questions you have on any new thread in which case, please start your question with, “ For FES only”.
That only applies to new threads, not this one. You have me exclusively on this one.