Many thanks for looking into my query and for your reply.
Sorry for not providing you the reference.
It is in the guidance for sponsors:
http://www.ukba.homeoffice.gov.uk/sitec ... sguidance/
para 446 (page 74) of the document titled Policy guidance for Tier 2 and Tier 5 sponsors - valid from 30 September 2011 says
446. We recommend that when you assign a CoS to extend a migrant’s leave, the start date you give should be the day after their current leave expires. For example, if the migrant’s current leave expires on 31 December 2011, the start date on the CoS should be 1 January 2012.
I discussed this with a friend of mine who argues that recommend does not mean compulsory. I do not know whether this argument is applicable for rules and laws.
I would be grateful if you could provide your expertise advise.