All seems very odd this.
Firstly, since when can a Captain defer his legal responsibility to ensure the safe operation of his flight as is required under his command.
Secondly, I've never heard of an accident caused by de-icing, there have certainly been ones caused by icing, so why take the risk ? If it was caused by commercial pressure then that is a Captain's decision.
What a truly bizarre and petty case this is. Anyone who knows even the slightest thing about Kegworth will see the foolhardiness of the situation. Hopefully the F/O gets taken to the cleaners.