Can I "point" an 0800 number at my mobile?

Yes you can. There are a couple of ways to do this.

First method:
A lot of people use a landline for business and divert it to their mobile when they are out and about. You can set up an 0800 number at a site such as:
http://www.the0800numbercompany.co.uk/

and point it at your landline. The 0800 number will follow any divert you set up on your landline. You need to check what the transfer costs will be from your landline to mobile - the charges can be hefty.

Second method:
Set up an 0800 number and point it to your mobile permanently. Set up fees, rentals and call charges are normally higher as the risk for the carrier is greater.