This may well be poor advice.
OP, just like the rest of this thread you should take what follows with a good measure of doubt. At any rate you do want to get reliable information by enquiring with the UK embassy or the Swiss government ( www.sem.admin.ch ).
Under old Swiss law the wife would automatically get the husbands's nationality upon marriage. Since holding multiple nationalities was forbidden she would lose her Swiss nationality.
Fast forward to 2006 when the current law became effective. These days there are no automatisms WRT citizenship, in particular each spouse keeps his/her nationality but may qualify for simplified Swiss naturalisation at some later point.
Now, there were multiple steps in the transition from old to new. But to cut a long story short, to remedy past discriminatory automatisms §58 of the law on naturalisation enables reinstatement of the wife's Swiss citizenship if she lost it due to marriage with a foreigner (she may have lost it, may have had to relinquish it, or may have failed to declare the wish to keep it, subject to when that happened and thereby what version of the law on naturalisation applied).
If your mother qualifies and applies for reinstatement of her Swiss citizenship, that would mean she was retroactively Swiss at the time of your birth which in turn would automatically give you the right to Swiss citizenship. The fact that you didn't register until age 22 would probably have no bearing because nobody knew you had that option in the first place.
Mind, what really applies depends on what actually happened, and when.
But the closing statement of section 2.2 in this federal paper (in German, sorry) tells me you definitely want to enquire further and get reliable information
"Conversely, the child can call on §58.1 if the mother was/is Swiss by birth and if her Swiss nationality has been reinstated after the child's birth."
"Hingegen kann sich dasjenige Kind, dessen Mutter nach seiner Geburt als gebürtige Schweizerin wiedereingebürgert oder aufgrund ihrer Abstammung erleichtert eingebürgert worden ist, auf Art. 58a Abs. 1 BüG berufen. "
Best of luck. And please report back on the reliable information you get.