UK's €1 trillion cash hoard - where?

Following from the post below, the last study I can find on the extent of cash hoarding by UK firms is from the Centre for European Reform, back in March, quoted in the WSJ. The CER is fairly pro-EU, but not uncritical. UK firms are holding an extraordinary €1 tn in cash, whilst the Eurozone nations' firms are holding €2 tn between them.

One can only sincerely hope that they're keeping the €1tn cash in bonds, gilts, the Post Office Savings Bank or under the MD's mattress - anywhere, in fact, but on deposit with the Zombie banks.