I went for the TP Link Ac 1750 router, which is available from Amazon at £69. Plugged it into the Virgin hub (which was switched to modem mode) and the difference has been incredible. Not a single issue since......and no more calls to the Virgin CS team (thank god!!).
I have been with Virgin for around a year and had similar challenges with wifi dropping out.....all due to the crap router. Purchased a "fit for purpose" router for about £70 and put the Virgin box into "modem mode". Now get 200Mb+ at all times with no drop-outs anywhere in the house.....works...