Why do most trading platforms require ID Verification? The vast majority of the Bitcoin trading platforms both in the US and the UK require some sort of ID verification in order to make Deposits/Withdrawals.

Is this because of these two countries current legislation? does this obey to some sort of policy?

Thanks.
In the US, these are called "Know your Customer", and "Anti Money Laundering" (KYC/AML) laws and is enforced by FINCEN (financial crimes enforcement network) in the US for any businesses that qualifies as a "Money Service Business" or "Money Transmitter".   

This guidance published on March 2013, http://fincen.gov/statutes_regs/guidance/html/FIN-2013-G001.html , makes it clear that Bitcoin exchanges must comply with existing regulation for KYC/AML.