Ring them and explain why you feel you should be excused, you may be lucky.
I have been on service several times and it was quite sad to see people with businesses unable to escape, asking to be excused in court, ( several weeks in one case, on duty. )
I luckily 'made' on the deal .. Court's loss of wages payment made up to full pay from employer .... The expenses were on top.
If no escape .. and actually on a case ( not mere reserve ) .. Refrain from any real liquid at lunch, you'll be hard put to stay awake .. Once the novelty has worn off.
You know how it appears to work? If tis a 'gangster' type case you will be relieved to hear your name read out as a prospective juror in court, at least once .. all eyes seem to bore into your soul.... oooer!
Then if chosen, end of day you may be leaving the nearby multi storey car park, finding yourself in a traffic queue with the defendants buddies surrounding your car as they await a lift ... Felt like pasting a piece of paper on windscreen 'Not guilty' .. Yep, they recognised me, nudges and winks... Was I glad to get moving.
Park well away from the courts !!
Good luck ..
England Expects That Every Man Will Do His Duty
Yeah right !!
Worth a glance .. perhaps.
http://www.cjsonline.gov.uk/juror/walkthrough/summoning/faqs/