At present, if you report your phone or sim lost/stolen, giffgaff put a block on your sim and then post out a new sim. Only this replacement sim can be activated back onto your account. The replacement sim can take a couple of days to arrive. This can be frustrating and inconvenient for the giffgaff member, as they must wait for the sim to arrive.
I would like to suggest that giffgaff consider trialling the option for a giffgaff member to chose a paid for Premium Sim Replacement Service.
Could use the strapline, "get your giffy in a Jiffy"
The Premium Sim Replacement Service would be optional and require the giffgaff member to pay a fee from airtime credit or a stored credit/debit card. The Premium Sim Replacement Service would use Royal Mail's Next Day before 1pm service. The charge would cover the cost of postage which at present would be in the region of £6.50.
I agree not all people would wish to pay this fee but many might to get their phone back up and running as for some, their phone is their business.
If giffgaff were able to offer a trial on this, then they could gauge support and interest and potentially roll it on a permanent basis.