Three flights a day apparently.
I remember back in the 1980s when Dan-Air did three a day on this route, Manchester to Heathrow (yes, Heathrow, into T1). This was when the route had way more passengers on BA than nowadays, and before all the huge APD etc. I took it once, they had managed to get about a dozen passengers on a One-Eleven. As you can imagine, it didn't last long. It was also about this time that Virgin also did "connecting" flights from mainland Europe into Gatwick, to feed their few flights they had then, using a Viscount in their livery chartered from BAF. That didn't last long either. Does nobody at Virgin remember ?
The thing about feeder traffic is that the revenue share the feeder operation gets is very low, and you need a good base of point-to-point as well to square the revenue. Also Virgin long-haul departures do not all leave together in a hub operation that suits a few inbound connectors, but are scattered through the day.
I wonder how Virgin think they will operate at Heathrow; as I understand it T3 has no facilities for domestic arrivals, even from coaching stands, so they will need to arrive at T1 and do a terminal transfer for any connecting passengers.