tamaris plc appears to have turned into world trade systems plc. whether your shares are related in any way to this new entity is another matter. try googling for the registrar of world trade systems plc and you can find out.
the ticker symbol for world trade systems wsl looks extremely illiquid, doesn't appear to have traded for years. I would guess there's not much going on at world trade systems at all
hi tec went private, so your shares were likely bought back at some point. so share certificate worthless? again worth finding the hi tec registrar to at least check what happened in regards to your certificate.
Yes, you should be able to take them to a broker to 'dematerialise' them. I think most certificates have been replaced by nominee accounts these days. Try Hargreaves Lansdown - they'll probably be able to dematerialise the Certs and convert into a nominee account for you.
I did some a while back, they charge a bit extra for certificates though.