Right, lets think this through logically.
Firstly declared interest of sorts - I used to be an apple fanboi but have got fed up of the strangle hold they have over everything, and gone over to android mostly.. You will do much better for your money with android phone and tablet- apple is very limited- no additional storage etc.
I use giffgaff and like it quite a lot. HOWEVER you will not be able to tether on giffgaf with an iphone (that's one of the apple stranglehold" features). You can only tether with iphone if the network is able to allow you to- and for this you pay extra. Giffgaff, unless it has hanged very recently , are not able to lift the the tethering bar.
So.... other options are many. My current choice would be either galaxy s3 /note 2 or google nexus 4 as the phone (I'm assuming you want a premium smartphone) and either a nexus tablet (the 7 might do you well) or the Note 10 inch tablet .(however the google nexus line are a bit apple like in than they don't have expandable storage, I have a 32GB card in my note 1 for instance!).
Not necessarily the best prices, just comparison:
32GB nexus 7 £189
SIM free S3 £387 (amazon UK)
Apple
Ipad mini £349 +iphone 5 £529
With the android option if 1GB data shared between devices is enough the Giffgaff £10 goody bag will do fine, if more you might be better going to 3 for more data?
Sorry that got a bit geeky but It fascinates me as my ipad1 is due for renewal when I finally get he ££ together. I love my note1 phones still. DS has a new nexus 4 that is great but I'm still a bit humm about no removable storage or removable battery (changing battery is primitive but so good on a long journey etc if you end up with no charge left!)