Overnight break on outward portion of return

[yorkie]

......without paying for the Tube.....

Firstly, I assume you are getting a train from Hayes & Harlington Heathrow as stated here:

. I can get to Hayes and Harlington as a permitted route to London (Paddington) and buy a return ticket to Heathrow from there

but that still leaves you a problem getting between Paddington & King's Cross, as the chances of LU staff at gatelines allowing you through are very slim indeed, and if you talk about your break of journey rights they are highly unlikely to agree that this would extend to the cross-London transfer.

I would give up on the idea of trying to use the cross-London transfer a day late and use contactless/PAYG between Paddington & King's Cross. In fact, unless there is a big time saving in going via Paddington which would likely give you an earlier connection into Newcastle, I'd consider using the Piccadilly Line tube direct (journey time 55min plus time to get to/from platforms).

 

[fandroid]

Firstly, I assume you are getting a train from Hayes & Harlington Heathrow as stated here:

but that still leaves you a problem getting between Paddington & King's Cross, as the chances of LU staff at gatelines allowing you through are very slim indeed, and if you talk about your break of journey rights they are highly unlikely to agree that this would extend to the cross-London transfer.

I would give up on the idea of trying to use the cross-London transfer a day late and use contactless/PAYG between Paddington & King's Cross. In fact, unless there is a big time saving in going via Paddington which would likely give you an earlier connection into Newcastle, I'd consider using the Piccadilly Line tube direct (journey time 55min plus time to get to/from platforms).

You are right, I was getting a bit carried away there. Journey choice is often tricky for that Heathrow to Euston or Kings Cross/St Pancras leg of my trips. It's a fine balance between cost, speed, and likelihood of getting an earlier train north. That means that even Heathrow Express is resorted to fairly regularly. The question won't arise this week, as I have been booked to fly to Newcastle from Germany (via Heathrow, where transfers can be hell, but it's too late to get it altered). I will always use Oystercard when appropriate, but like to use the cross-London part of return tickets when it makes sense.

 

[Greenback]

There isn't really much between using Heathrow Express followed by an onward journey, and using the Underground direct to Kings Cross. It can be influenced by conditions on the day, and, given the difference in cost, I'd almost always go for the tube.