Got my confirmation email, tracking details and can now access MyO2. I also now have an account and phone number. Been having a look at what you can do online, and at first glance, it does seem you can drop the data bolt on quite easily. Shows an option to manage bolt ons,, with a swap button. The choices are then basic, 6£ option, £10 option and none. There is then a message that if you choose none, you will be charged on the up to 50mb a day at £1 rate.
So if that is the case, you could knock off data taking a further £70 or so off the total for the phone, which breaks down like this:
149 for handset
5 for accessory (quidco or topcashback is for new contract plus accessory)
1 x13.50 and 23 x 10.50 = 255
Total is 410 which is only a tenner more than the payg offer - then minus 100 from topcashback or quidco leaves just 310 for the phone.
Will keep you updated