The cabin baggage security regulations which apply to all departures from any EU airport (irrespective of the destination) are here:
http://www.dft.gov.uk/transportforyou/airtrave l/airportsecurity/
Virgin's own rules about baggage are here:
http://www.virgin-atlantic.com/en/gb/passenger information/baggage/index.jsp
(Use the links down the left, as well as the FAQs section).
Virgin Atlantic close their check-in desks 60 minutes prior to take-off. They currently recommend checking in 2� hours before take-off. If you aim to allow 3 hours, you could be delayed en route to the airport for up to an hour and still check-in with no great rush.
Chris