Do I have to have specific Nordic poles to take up Nordic walking

I have Brasher trekking poles, I can't see much difference compared to the Nordic poles. The main difference is the application of the pole. in trekking more weight is taken off the leg joints by the poles and in Nordic walking they are use to drive you forward. If used correctly both should have straps that take the load keeping a loose grip on the pole when swinging it forward. So, if your poles have straps, I see no reason to invest in any more. Although, some of the cheap trekking poles have thin straps that are very uncomfortable over a long period, the strap should comfortably take your weight without digging in to your wrist.

I would use walking poles and just get walking. I hope you have some nice scenic walks.

I notice that Nordic poles have special feet - I think they call them 'paws' to enable them to drive forward. Is it possible to adapt ordinary trekking poles by removing the normal ferrules and replacing them with the 'paws'?

I think you can buy those angled feet to fit any pole.

I will have a look in Decathlon when I'm next in Stockport.