Is there not a way you can add coins yourself? Like the 2012 10p? Or do you need a kit?
Depends on the mech in question, but generaly you do need to send em off for re-calibration.
However, I know andrew96 over at Classic Reels (Mr P's Amusements etal), found a crude hack on the MARS Cashflow 126 series mech's, where it was possible to use one of the programmable token lines on the mech, to deal with the steel 10p's you talk about, but long term, you realisticaly do need to send them off to be re-programed.
I do have a contact in Leicester area, that offers a service for reprogramming mechs, from £15 delivered (Dependant on the mech, but most MARS / MEI mechs are done at this price), and this is for ALL coin lines on the mech, not just the 1 line etc you normally get at this price.
All UK coins from 5p up to £2 covered, and this includes the new steel type 2011 10p / 5p's.
All MARS / MEI ME 1xx and Cashflow 126 mechs are covered.
For MS 1xx mechs, these can be done, but due to the tight tolerances on this series of mech's, it may not always be possible to adjust to the steel 10p / 5p's.
Cashflow 126 Mech's can be done with no issues, but other Cashflow mech's are not always possible, however in any case, you are advised to forward the make and Model number of the mech concerned, as this can then be used to see if it's possible to do or not.
C335 / C435 / SR5 (Coin / Cash Controls), can also be done at pretty much the same terms
Anyone interested, drop me a PM, and I'll forward you the chaps details.