Upvote:2
There is definitely a risk attached to trying to use a short-term study visa granted for a specific internship to enter the UK as a visitor to attend a totally unconnected conference.
Immigration Rule 321A (1) provides that a personβs leave to enter may be cancelled at port or while the holder is outside the UK if there has been a change in circumstances https://www.gov.uk/guidance/immigration-rules/immigration-rules-part-9-grounds-for-refusal
It would be advisable to contact the embassy that issued your visa to ask if your change of purpose of travel is acceptable.