The 'nice' vat man works out your turn over over a rolling 12 month period if at anytime this goes over the threshold then it's time to register. One advantage is you can claim back up to 5 or 3 (can't remember) years worth of purchase on your 1st return, but that is probably about the only time you will get anything out of them!
I would be very concerned about running 2 vans doing the same job from the same premises etc, like Steve said if you set up one as a ltd company, that then would be its own legal business, surely it would be an advantage to register for vat and group it all together, but you know your own business the best. I don't think they allow you to trade as 2 different business's offering the same service, thought they had closed that loophole, as Cameron needs all the money he can lay his hands on !
Billy re your ironing service.....my thongs had stains on them when you returned them...could you through some light on this please