Jury service

I know it is my civic duty to do it, but based on the leaflet accompanying my citation, I'm wondering on which of the following grounds I could make my excuses:

currently detained at her majesty's pleasure
a prison officer
a member of the House of Lords
a person in a holy order (why do the nuns get off?)
a sherrif
on bail in connection with criminal procedings

I don't think my recent conviction for driving without a seat belt counts.