Thanks for the advice, and apologies for not getting back to you sooner; I've a busy life.
Everything seems to be working just fine. I decided to 'splash the cash' and go for the Samsung Galaxy S5 instead, and it hasn't disappointed me at all. The micro-SIM arrived a day earlier than was quoted, and the bloke on the other end of the phone was extremely helpful and pleasant to talk to. Great service as usual from you folk at Virgin.
If you could let the guy on the other end of the phone now he has my thanks, that'll be awesome.
I have a 12 month sim-only deal with VM at the moment. The sim card I currently have is standard size. I'm inheriting my daughter's Samsung Galaxy S3 which requires a "hybrid SIM that can be used in Micro and Nano SIM phones." I understand from the early responses in this thread that I can buy the sim I need from VM for £2.99 including first class postage, which is fine.
My question is this. Will I continue to be able to use the normal size sim in my old phone once I have activated the hybrid sim in the Galaxy SIII. Obviously, the number will be the same for each Sim. Thanks.