The fact of transferring the money by itself - is not taxable event.
If you will repay back to your parents - that the transfer is the loan.
If you are not required to pay back - the transfer is a gift. For you as a recipient of the gift - the gift is not taxable income regardless of the amount. The donor might be required to file a gift tax return if the value of the gift is above $13,000 (for 2009) per person per year.
If your parents are not US residents they are not subject of US tax law and are not required to file the US gift tax return.
In UK - if your parents make a gift of an asset they will be treated as if they had sold the asset at its market value. Capital gains tax will be charged on any increase in the value of the asset since they acquired it.
Please see more details here - http://www.hmrc.gov.uk/CTO/customerguide/page6.htm