Assets held before the marriage

Say I had shares in my own name before the marriage.

Does the STBX have any claim on them?

In England after a medium length marriage the answer is yes.I know this to my cost.I also owned my own home, STBX had nothing ,now he has a good job,income, I have a small pension but my pre marriage home/savings/investments are part of the Marital Pot.
The Law may be different in Scotland

The marriage was only for 3 years - is that short or medium?

I would say that was short.

My partner had an FDA in January, STBX wants 50% of the property he owned before they got together, they were only married 2 1/2yrs. the judge (district) in January said she''s not entitled to 50% it was a short marriage, but yesterday he went back to court for what was meant to be an FDR and a different judge (deputy district) said she gets 50% of the property before any debt is taken from the equity... even though she lived there for 18mths made minimal contributions before they moved to another country (partner returned to his property when they separated)

I don''t know what to believe now, it goes to show the opinions different judges have

In Scotland the length of the marriage makes very little difference, usually only the assets accrued between the date of marriage and separation form the matrimonial property to be shared.

If you had shares in your own name before marriage and your have kept them separate from the family assets they would be considered non matrimonial. However, if you had shares and sold them and the proceeds became incorporated into the family assets they would be considered matrimonial.