Can my US Roth IRA and 401 K be transferred to the United Kingdom?

I have been living in the US for 9 years as a perminent resident - and am planning on moving back to the UK where I have citizenship. Will I be able to transfer these funds to a similar institution? Also what will happen to the social security I have accrued? If there is a link anyone can send me (sorry to be so long winded!) - Chloe