58 in a 30 in N. Wales?

That's asking for trouble, mate. Presumably you've been summonsed by now? I'd go to
http://www.pepipoo.com and ask for help on the forum there. They're probably the best place to ask about combining the two NIPs as well, though I think 4 minutes apart would probably make them far apart enough on the road to be separate offences

. Try to get as much info out of the police/partnerships as possible and ask for the photos and/or videos as well. The more you can give Pepipoo the more chance they'll see something that might give you a chnace at fighting it.
You might also want to check out
the road law page on www.lawontheweb.co.uk and the
Association of British Drivers who have a legal advice helpline and a list of lawyers around the country who can help with speeding offences.
Good luck, and if you do end up 1 ticket from a ban you might want to get an OriginB2 and go very carefully for a few years.