To weaken encryption procedures in common sw is a bad idea over so many aspects, mainly because technology is agnostic wrt who uses it or tries to break it.
Worse than that, I'd argue, would be having one government purposely weakening encryption of one or more sw products produced by third party companies that, of course, sell that product worldwide. The market gap that would originate from that would probably screw up the tech balance quite badly - either by imposing additional costs over these sw houses (that may therefore stop licensing the sw in the UK entirely), or by externalities toward other users of the technology (that even without being in the UK would find themselves affected by that decision).
It's a tough matter and it should not be treated lightly - as modifying the current state would not only affect on government actions/policies and security, but also market, technological, and international issues, with a dangerous snowball effect.