I was thinking of changing the connections to the hot water cylinder
from an indirect to direct feed. Can I do this to my existing cylinder
or, because of the increased pressure will I have to fit a new one.
Thanks for your input

Its the 10mm tap tails that are your problem. No way round that other
than to fit different tap.

Or to increase the pressure, as the OP intends. Obviously, the initially
proposed solution of the OP to convert the existing gravity cylinder would
be extraordinarily dangerous. However, the principle is sound (provided the
cylinder is replaced), provided the mains water supply is adequete.

To do safely, it would require the replacement of the hot water cylinder
with either an cylinder unvented cylinder or heat bank. This will cost a
considerable amount of money, but would have significant additional
benefits. The shower, for example, will be exceptional, without the need for
pumps. The bath will fill rapidly. Bulky cold water tanks that are
succeptible to freezing are no longer required in the loft. In the case of
the heat bank, the hot water becomes potable, so can be used in the kettle,
or even directly for hot drinks.

Christian.