Since 4th May 2006 (in Scotland) a father has automatic parental rights if he jointly registered the child's birth with the mother.
If your ex has a residence order for the child she can take him out of the country for up to one month without your permission (e.g. on holiday). If she attempts to take him out of the country for a longer period (e.g. to emigrate) she'll be committing a serious criminal offence.
If your ex does not a have a residence order she needs your permission to take your son out of the country (even for a day trip). Again, attempting to take your son abroad, without your permission, is a serious criminal offence.
See here for further information about parental rights:
http://www.direct.gov...entsRights/DG_4002954
(Note that the qualifying date of 1st December 2003, on that page, refers to England. I've given the correct date for Scotland above).
The reference to 'confidential information', in that link, suggests that you have the right to see your son's medical records.
Chris