Bike respray

Another vote for Mercian here. They did a frame for me years ago. Superb job. 
The company was saved last year by four Derby cyclists buying it when they looked set to close to allow it to keep going, with Mercian's enviable reputation (even fashion designer Paul Smith has Mercians) so to keep them going I would use them (use it or lose it)

I would strip the frame completely, wrap it carefully and send by a reputable courier to Mercians. As said not in the South but the skills and knowledge are out of the SE for such artisan perfection. 

An alternative choice would be Woodrups of Leeds who also bought up Bob Jackson's a former competitor, when that was closing down a few years ago. They do some mean frame finishes and all these companies are far better than attempting amateur DIY resprays. 

Post the frame to Mercian in Derby.  Especially if it's metal.  Then chat to them about colour.  They can use your decals and may be able to source some for you.    Great value IMO.  It may take more than 3 weeks.  They have done two for me - one vintage British and one modern.  No they're not in the south, but Parcelforce is not pricey for a frameset.  Also, if it's a metal frame they can fix issues or modify with braze ons etc for a nominal cost.

Have you thought about doing your own respray?  I did my old Cube, using "Spray.bike" powder coat rattle cans.  I was really pleased with the results.

If you're happy with just orange or black then XO bikes in Wandsworth and Lewisham will powder coat your bike.

The work is done by former offenders as part of training to help them with life outside prison.

Pretty much all roads in the south lead to Argos, but beware some long lead times.  

It does help to talk to them in person with the frame.  If it needs anything like Raleigh head badge holes filling in, broken threads fixing, or alignment work, it all adds up.  

I mailed one to Mercian a few years ago - the shade was way off what I thought the swatch suggested, but it's a good job otherwise.

Portsmouth: but I don't know who does the work, or if it's just as easy to go to a LBS nearer you. https://gcbikerepairs.com/pages/frame-resprays?

Powder coat Eastleigh - you may well have somewhere nearer.  A lot cheaper of course and I got a decent result with a steel lugged frame.  http://www.solentpowderfinishers.co.uk/contact/

please post back if you go ahead with anything 

If you haven't already, consider searching for powder coaters, too. I just got mine done (in the USA, sorry) and am very happy. They can do gloss and candy in powder coat now, so it's not just the nearly matte look of a Surly frame.

I can highly recommend Argos (not the shop), rather Argos Racing Cycles in Bristol, I couldn't be more happy with the restoration frameset they prepared and painted for me a few years ago. 

I suspect this is not what you're after but, just for fun, have a look at Fat Creations. One day...

You could try Winston Vaz at varonha.co.uk I know a couple of people who've had refurbishment work including respraying done by him. He's based in South London