The bad news is that, living near London, I've had the vast majority of my "serious" colour prints from mF tranparencies made in the USA for the last five years. Whenever the selling price can reflect the costs including Fedex charges, and the inevitable longer timescales, my stuff goes to California.
Like you I've explored a number of alternative routes to reflect the fact that sometimes I just can't cope with the time or cost of having Tango scans and LightJet prints together with the transport of transparency, proofs and then final prints from the US.
For a "custom print" solution, you might consider Bayeux at 78 Newman Street W1 ( runs north from Oxford Street between Oxford Circus and Tottenham Court Road). They have a LightJet and a drum scanner ( though not I believe a Tango) and whilst in my view they are not quite up to the standard I get from the likes of WCI they are decent. Not cheap though and a drum scan plus (say) a 20" x 24" print will cost about £100 with VAT.
For cheaper, faster solutions I've tried BPD's Ilfochromes, Peak Imaging and Bayeux' Frontier Lab, BX2, sending each in turn the same few medium format transparencies and the same brief. In general I thought that the BPD prints came out worst with one being very poor indeed. I guess I always tended to believe that low cost Ilfochromes were unlikely to be great. The Peak prints (I paid for their "custom" product) was better but still not good enough for me to want to hang or sell them. The BX2 Frontier prints were the best of a mediocre bunch and were reasonably priced. All of these people fell down on at least one of the images I sent them. The best quality overall is from a Frontier that will print only to 15" x 10" which is smaller than I sometimes like or need and is unlikely to handle the dynamic range of a contrasty tranny well since the scanner isn't the best.
I gave the same material to a friend who made scans and inkjet prints that were in my view better than any of the lab prints I got. But I don't want inkjets.
I'm seriously considering at this point buying a film scanner and calibration kit to make my own files that I can have printed wherever according to my timescales and budget. I just don't think that low cost commercial solutions are going to give me what I want/need.