Whatever rights you have to work in the UK on your vis will continue till a decision is reache on your application. You will need to submit a copy of your previous visa along with the certificate of application that would have been issued by the UKBA.
Your employer will then have to fill out a form with the details and send this to UKBA by e mail who will send a confirmation within 5 working days. Make sure that they mention the reference number from your certificate of application in section 2 of the form. You can direct your employer to the following link
http://www.ukba.homeoffice.gov.uk/busin ... /ecsstep2/
Once they have carried out this check they are covered for a period of 12 months and will only need to repeat this procedure after 1 year. That is if you have not yet provided them with your updated visa by then. It is a very straightforward process and