The E-145 isn’t certified for London City, so it won’t be that. It might be the Stobart operated E190s with the Virgin australia cabin? These are ‘normal’ BACF services and you won’t be able to change for free, I don’t think.
The E135 is certified, but I these are few and far between. I don’t think anyone I’m Europe operates them - Luxair and bmi Regional used to. A little Irish start-up called jetMagic used them from Cork to LCY, but I can’t think of anyone else.