Instructions:This is my first post so hope it works for everybody.
Ordered a nokia 1112 cost £25 and added 3xFREE Tesco Mobile Extra SIM with 1/2 price Airtime Voucher Pack (£10 each for £20 credit) to bring order to £55 delivery is £5 but is discounted automatically.
Used TDXR-DTD50 for £10 discount off £50 spend.It said I could only use 1 TDX voucher code so I tried another - TDR-5LDTD5 for £5 off £50 spend and it seemed to accept it as well when my order was processed at checkout.
Phone and £60 credit for £40 including delivery. others have said you can transfer credit to existing phones although i haven't tried this yet so i cant confirm.