Hi there, apologies for our late response.
I can confirm the restaurant at this hotel is a Thyme.
The serving times are stated in previous comments.
I hope this helps.
There is a restaurant on ground floor. But we didnt try any lunch or dinner. There are many restaurant around this area.
As noted it's Thyme Restaurant. Their menu is pretty standard hotel fare and on the slightly expensive side. However it's convenient being part of the hotel. However there are so many great restaurants in London that it seems a pity to eat in a hotel! If you go to the Premier Inn web site and scroll down to the bottom of the home page there's a link to "Food & drink" which will take you on to a page where you can look at the menus and prices.
Thyme restaurant which is on site. It has always proved to be a good place to eat.
Get an answer from Premier Inn London Euston Hotel staff and past guests.