Could someone tell me if 1hr 45 minutes, is long enough to change planes at Heathrow? Delta international flight to Virgin Atlantic domestic? Thanks
Minimum connection time on a single ticket for those flights is 90 mins,so you are inside that. Follow the connection route in T4 airside for immigration in T1. Don't go through immigration in T4 and do the land-side terminal connection. If you do misconnect, eg late arrival,on a single ticket you will be put on the next available flight.
Marco's point is key. Have you booked this as a single ticket or are you booking as two separate tickets?
If the first, you are ok as the carrier is responsible for getting you to your final destination. If the latter, then you are on your own (e.g. could have to buy a new ticket) if your first leg arrives late and you miss your connection.
I will have to say that I've decided to never travel on two tickets again - we did that in June coming from Copenhagen to Heathrow and from Heathrow to SFO. Of course, our plane from Copenhagen was late - we had to run for our Heathrow flight (that was boarding)(we were supposed to have 2 hours to connect). We had our 2 granddaughters with us so felt a bit of stress with this arrangement. We did make it, but I don't want to do again.