f I enter on visa exemption with UK passport I get 30 days in Thailand. If I travel to Philippines for a month during the 30 days then back to Thailand do I get another 30 days?

No problem, whatsoever

Assuming you have not already spent very long periods in Thailand as a tourist, this will be absolutely no problem.

When you arrive airport in Philippines check with your airline if  onward flight is required for your return flight to Thailand. 

17 hours ago, joethejobber said:

f I enter on visa exemption with UK passport I get 30 days in Thailand. If I travel to Philippines for a month during the 30 days then back to Thailand do I get another 30 days?

Should not be a problem. In fact, a lot of people stay for the 30 days and then go to another country "for a day" like Laos or Cambodia but quickly realize they prefer Thailand so they hop right back across the border into Thailand, sometimes within an hour of leaving, and get another 30 day stamp !

I did this once about five years ago.  I was up in Chiang Rai so I just went north and crossed into Laos.  Spent about an hour there and then came back and got another 30 days.