hsbc legal mortgage: why do they want power of attorney?

[afussyphase]

We are re-mortgaging our house, and have been offered a mortgage. On reading the terms and conditions, point 18 reads (I'll summarise in [ ] so as not to run on and on):

"You [both], irrevocably (until [Debt is paid]), appoint the Bank [and/or its receivers] as your attorney. This means the Bank and/or each receiver can:"
--sign and deliver documents
-- exercise powers and do any act in respect of any of your obligations under the Mortgage;
-- make payments, renew insurance, carry out works, represent you, do other things (including entering into any new lease ...), or bring, settle or defend any proceedings (including forfeiture proceedings) in your name .. etc etc.

(Some items are paraphrased as I'm sure you can all tell).

Why does HSBC need or want these powers? It seems to indicate that they could, well, carry out works on our house, entering into leases on our behalf, and so on -- since that is what it says. I do not want HSBC to actually have power of attorney, as I understand it, but perhaps I do not understand it.

In any case: what should we do? It seems unlikely to me that they really need what I consider to be power of attorney. Any advice much appreciated!