Here's the Dylan Thomas one, not a very clear example, unfortunately
Roy Plomley was born in Kingston, Surrey.
Barbara Ward was born at Heworth, Yorkshire
Joe Mercer was born in the Wirral
Kenneth More was born in Gerrards Cross, Buckinghamshire
Dylan Thomas was born in Swansea
Sir Alec Guinness was born in London
Joan Littlewood was born in south London
Abram Games was born in Whitechapel, London
Max Perutzwas born in Vienna, and
Noorunissa Inayat Khan was born in Moscow.
I don't know whether the postmarks will be applied on mail going to their birthplaces or the places where they are best known, or did most of their work. Time will tell!
Royal Mail have provided these mock-ups for two other postmarks which are being used for Noorunissa Inayat Khan to London WC1 and Roy Plomley to the KT (Kingston-upon-Thames) postcode area:
The Dylan Thomas slogan is in Welsh this week and English from March 31st, on all mail addressed to Wales.