Hmm... you can get 0871's for free that redirect internationaly, even to some mobiles. OK, it's not the cheapest prefix, but it's better than 070! (eg.
from here - click Description, then Which Service do I Need? [disclosure - affiliate link])
Years ago, back when they very first became available, I used to have an 07050 number i gave out instead of my mobile, but now just have a redirect-on-no-answer on the home phone, since thats the number people actually call us on, and I'm happy to stand the cost for the few calls we actually get. I used to run some 0870 numbers, too, for an online business, and that was specifically because when the phone rang, I could then tell what the number dialed was, so could answer approriately.
As it happens, back on topic, the washing machine bloke I use (twice..) also has an 070 number, and as a tradesman, I've found him very reliable, and fairly cheap.. I'll have to educate him about the call costs should I need to contact him again..