Claim 'Physical and Psychological Abuse'

More bombshell allegations in the world of international gymnastics -- with 17 British gymnasts alleging "systemic physical and psychological abuse" from British coaches.

The group of women -- which includes 3 Olympians -- issued a notice to the British Gymnastics association spelling out plans to take legal action.

The group -- whose ages range from 15 to 43 -- allege coaches grossly mistreated them while implementing an iron-fisted "winning at all costs" mentality ... which included the use of physical force against athletes as young as 6-years-old.

In the notice, the women claim the physical abuse included "inappropriate use of physical force by coaches against gymnasts constituting…