A bit OT but the idea of no accent is kind of funny. My kid goes to an international school in Thailand. I hear my kid's classmates speak English with Australian, British, Canadian and northeastern American accents plus an accent we call "international school accent". I'm from California and of course I think I don't have an accent. Same as those kids and their parents. Yet I have a hard time understanding some of them.
Well, you can't literally have no accent. I think that the GP means that there is no 'tell' that the people are eastern european when they speak.
In the UK itself, it's estimated that there's a different regional accent every 25 miles or so.
I'm English and live in Lithuania now, and many of my Lithuanian friends can speak perfectly good English without an 'accent'. It's also not uncommon to speak a third language like Russian or Polish, especially if the family has their roots in that country.
These languages do have some shared sounds, but are definatly not just dialects of each other.