Hard to say without seeing it, as it depends on the state of the rest of it.
Certainly there is no doubt that new sockets in the conservatory (well, anywhere actually), and any new lighting wiring , will need RCD protection somewhere to be regs compliant.

Existing work has a much lower bar to pass, generally only needed to  meet the regs at the time it was installed, providing the changes since then do not mean it would nowadays be considered an immediate danger. 

(If you would like a more homely example, driving a  1970s car is not illegal if it does not have seat-belts, of course it is not as safe, but not considered such a great  danger it must be banned, but you cannot market a new one like that ..)

The current advice is that wiring  pre-dating RCDs is not an 'immediate danger', just firmly an 'improvement is recommended' Do be aware though that over time the advice about this sort of thing moves one way only... stricter ;-) One day it will be disconnected....

The fastest way to do this may well be a new consumer unit, but a mini CU with modern RCDs in it just to cover the new stuff supplying the conservatory might be an option, if you have somewhere sensible to put it.
But that may not work out any easier, and if there are other aspects of the extant building wiring that need attention, such as rubber covered cables, or lighting with inadequate earthing, then this will all need correcting too.
By all means post a bit more description and we can advise better.

Mike

errata

the seat belt law in the UK came in 1966 that cars had to have provision for them in the front.
Not using them in cars so equipped became an offence in 1983 - about the time I was learning to drive. It now feels quite odd now to visit a country where they are not required.

RCDs for new sockets supplying equipment for use outdoors came with a regs update  in the mid 1980s, and another in July 2008 extended this to pretty much  all new general use domestic sockets.

There are quite a few non RCD installations around still but they are certainly getting older.

Mike.

errata

the seat belt law in the UK came in 1966 that cars had to have provision for them in the front.
Not using them in cars so equipped became an offence in 1983 - about the time I was learning to drive. It now feels quite odd now to visit a country where they are not required.

RCDs for new sockets supplying equipment for use outdoors came with a regs update  in the mid 1980s, and another in July 2008 extended this to pretty much  all new general use domestic sockets.

There are quite a few non RCD installations around still but they are certainly getting older.

Mike.