Giffgaff's T&C's are very clear about it being for personal use only and not for business use. Also, not wishing to sound harsh but if you relied upon your mobile for business you should probably keep a spare PAYG SIM on a diverse network for added resilience.
"3.5. Your use of the Services must be for your private, personal and non-commercial purposes. You may only use a device with an IMEI number associated with it on the Network and you will not use or permit anyone else to use your SIM Card:"