The Visa EXEMPTION is 60 days, it may or may not revert to 30 days, if you enter the country the day before it changes you will get 60 days, feel free to ask the immigration officer if you can have 60 days because you bought the ticket so long ago, they can probably do with a good laugh at the moment.
IF it goes back (big if) and it's before you travel you are better off applying for a visa online before departing the UK, London embassy is super fast, 4 or 5 days, and you won't waste a day in a Thai immigration office, also airlines can refuse to allow you to travel if you don't have the correct visa, very unlikely but possible.