Postal address validation – special characters

We are currently looking at adding validation to our form that enables users to enter an address manually if they don't/can't/won't use the postcode lookup software

99% of our addresses will be UK but I am struggling to find any definitive article/paper that tells me what special characters are NOT permitted in address lines.

There are obvious characters that are permitted (eg: forward slash to cater for c/o) but we want to make sure our validation is correct and standard