I have used Giffgaff a few times when travelling to the UK and found it works very well. Since you will only be there 9 days I would suggest buying a Pay as you go plan. If you are not doing a lot of on line gaming or watching movies on your phone then a plan with 1 gig of data is available for 6 pounds. You can set it up on your phone a couple of days before you arrive then it will be ready to use after you turn airplane mode off when you land.