We did think about changing dates, but the hotel we have booked in Vegas will not change the dates for us, so we would have to rebook the hotel.
On the Virgin Atlantic website they have a page giving you your rights under EU regs 261/2004. If your flight is cancelled, they say you have 3 choices. One choice states:
To take an alternative flight, under comparable transport conditions, to your final destination, where seats are available, at the earliest opportunity.
To me, with my understanding is that:
Virgin are to assist me in getting to my final destination as soon as possible, not 24 hours later.
They must get to to my final destination (Las Vegas), not Los Angeles, San Francisco, Washington, or anywhere else they choose.
Under comparable transport conditions indicates that I could ask to be placed onto the direct BA flight from Heathrow. I am fully aware this will cost more for Virgin, so I believe my request to fly Virgin via San Francisco, then onwards with Virgin America is, and should be acceptable.
I appreciate all of the comments, and it is beneficial to understand how others read into our problem.
What I find most annoying is that when I called Virgin customer services the other night, the person I spoke to said he would be happy to transfer us onto flights to Las Vegas via San Francisco, but as we booked through a travel agent, they would have to make the request on our behalf. My travel agent unfortunately has not received the same response.
Many thanks once again