The train to Euston from Manchester is fine, the pain is getting to Heathrow. I don't know where your office is, but if a taxi from EUS plus the PIC-EUS train is priced similarly to getting the plane, then I would seriously consider it. Train-tube-train-taxi is fine for those of us with less cash and more time, but may not be ideal for a commute. It's a lot easier to work on the train than it is on a plane IMO. So that's another aspect to consider.