I understand that my pension is frozen whilst in Thailand but I gather that if I returned to the UK for  a short visit I can get it up-rated whilst in the UK. Does anyone know how this works? I presume I would ring the DWP and tell them I am coming back but what will they ask me so that I can have the relevant information to hand.

And don't tell 'em you are coming back here.   555

There is a recent article about this here;

https://www.thisismoney.co.uk/money/pensions/article-10786301/Can-state-pension-unfrozen-visit-UK.html

It was very simple when I did it. I thought that they might give me a hard time, but they were very helpful. Just give the International Pensions Service call in the UK (I did it after I arrived in UK). The guy asked me my NI number, arrival date and my departure date, and informed me that I would receive the uprate. A letter arrived at my overseas address a few weeks later to confirm the payment.   The IPS number is +44 191 218 7777

Thanks for that, most helpful for me and I hope for others, everyone should take advantage of this when returning.

Ring them once you are in the UK. They will take your details and send you confirmation to the address you gave them with your pension entitlement if you are in the UK. As to whether you advise them once you leave the UK to return to Thailand is a matter for your own conscience.