Is hardwiring a legal requirement for pumps + lights in UK?

I currently have a double weatherproof socket (MK masterseal) that has a
built in 30mA RCD by my pond which was installed by an electrician while my
house was being extended. I am wondering if this was the appropriate
installation as my Hozelock pump says that it is intended to be hardwired to
the mains, does this mean that it should only be used with a weatherproof
switch type box, would this apply to most if not all pumps? So should the
electrician have known this and installed a weatherproof switch instead of a
double socket (he knew it was for pond equipment)?

Thanks for any advise,

Will