Currently I am married in the UK for 40 years although the wife and I have not shared a bed for over 15 years. I am now with a Thai lady for 3 years and marriage may come up in the future so my question(s) are as follows.

In Thailand do I have to be divorced to marry a Thai lady or is the seperation enough? Is there such a thing as "legally sperated" and if so how do gain this position?

Any help or thoughts on this would be helpful, even if it is the seay answer, get divorced ( often easier said than done.)

Yes, there is such a thing as 'legally separated.' It's usually referred to as divorced!

If you wish to marry your new girlfriend you have to divorce your wife first. Neither Thai law nor UK law will recognise the marriage if you don't.

Also, whilst I am not sure of the situation in Thailand, if you were to marry your girlfriend in the UK before any divorce then the UK would consider that marriage to be bigamous, which is illegal; do you like prison food? If you married her in Thailand you would certainly not get a spouse visa for your new Thai wife if you are still married to the old one.

Where did you marry? If in Thailand you can divorce in Thailand or the UK; if in the UK then (I think) to have the divorce recognised in the UK you have to divorce in the UK. This means going through the courts, but if your wife is agreeable and the divorce uncontested this can be a simple, fairly quick and relatively cheap procedure. Talk to a matrimonial solicitor.

7x7 ( size of my garden) thanks for that, it is I had suspected. Could anyone do with 1000 bts and has abit of time to kill in blighty

If you originally Married in the UK? you would need your "Decree Nisa" and "Decree Absolute" document from the UK Courts,and If I remember correctly also a "Affirmation of Freedom to Marry" document,both documents checked by the British Embassy.

That is Assuming you intend to Remarry at the local Amphur.