In reply to Big Jim The Climber:
You can search for any ML assessment course being run in any area you want. ID the provider and then contcat them to see if they will do your re-assessment.
http://www.mountain-training.org/find-a-course
FWIW I think you'll find though that your half day will actually be a full day re-assessment and you'll be quoted/charged accordingly by the provider i.e. it's a days work for them as they won't be able to do anything else that day.
Also nav re-assessments will usually take the best part of a day whilst the assessor satisfies themselves that you are at the required standard.