" Calls to 03 numbers cost no more than a national rate call to an 01 or 02 number and must count towards any inclusive minutes in the same way as 01 and 02 calls.

These rules apply to calls from any type of line including mobile, BT, other fixed line or payphone "

http://ask.ofcom.org.uk/help/telephone/03number

So a 01/02 alternative would be of no benefit to you.

Additionally, from the firont page of this site:

"The site lists inclusive, geographic rate or free numbers for many well known companies."

"Search on an expensive 0842, 0843, 0844, 0845, 0870, 0871, 0872 or 0873 number to find an inclusive or geographic rate 01, 02 or 03 number or a free 0800 or 0808 number."