Great to see another Japes Trip Report. I must file the T5 Premier Inn for future reference... I normally use the T4 one and use the Lizzy Line/HEX to change terminals as I find it less of a faff than the bus. But if the 423 is regular and reliable then I will have to try it out next time I overnight at LHR.

PS - fully agree on Premier Plus, similar to you it was less than £10 more at T4, but unlike you I make use of the coffee machine to avoid the Costa coffee (he says currently drinking coffee from a Costa! ).