not sure on the building side but as a guide the notification for gas work can be done to either the customer or as i do the certificate is sent to me (to do so i have to fill in page 2) the reason i do it has nothing to do with payment just i like to have a copy of the cert in case of dispute over its issue.
i copy it then send the original to the customer usually about 2 weeks to get it and then a week for me to forward it on.
because i do this i recently got a customer out of trouble as he was selling and had mislaid the original (a faxed copy was sent to the buyers solicitor and everyone was happy.
as for payments i would expect you to withhold a reasonable amount if work was unfinished / needing remedials, but it should be proportionate to the work.
holding £3,000 for £500 worth of work would be unreasonable but 50% on top of the agreed money wouldn't in my mind.
i copy it then send the original to the customer usually about 2 weeks to get it and then a week for me to forward it on.
because i do this i recently got a customer out of trouble as he was selling and had mislaid the original (a faxed copy was sent to the buyers solicitor and everyone was happy.
as for payments i would expect you to withhold a reasonable amount if work was unfinished / needing remedials, but it should be proportionate to the work.
holding £3,000 for £500 worth of work would be unreasonable but 50% on top of the agreed money wouldn't in my mind.