Hi Tim.
I have an MIA and and an MIC. Broadly speaking the MIA is the UK based award for teaching summer walking, mountaineering and rock climbing whilst the MIC is the UK award for the same activities in winter.
All of the awards follow a similar route: Prior directly relevant experience, register with one of the MLT boards (England, Scotland, Wales or NI as appropriate), attend a training course, gain further experience and attend an assessment, record ongoing experience and cpd.
The starting point for any of the higher awards includes holding the Summer Mountain Leader award (the award for supervising hillwalking groups on non technical ground in the UK. Whilst your UEL would not be recognised as part of the current process of obtaining this award for people like yourself with extensive experience it is possible to apply for exemption from Training. I would however recommend a refresher as a minimum before Assessment to make sure how you work is in line with current thinkings on good practise.
The MIA and MIC are awards with a large component of climbing and are directly relevant to UK conditions and venues. If you are looking on something more in the trekking line I also hold an IML. This is an internationally recognised award for leading trekking parties in 'rolling Alpine terrain' (non glaciated) 'without the tools of alpinism' (i.e. the leader can carry an axe but the group would not normally be expected to carry one or crampons, likewise ropework would be simple emergency ropework or that needed for short sections of chains or other fixed gear on otherwise walking routes- not Via Ferratta). More details here: http://www.baiml.org/
For the UK based awards as the other poster said the MLTUK website is the place to go. This chart shows how the awards fit together: http://www.mltuk.org/awards.php
Al