Upvote:1
UK visitor visas are routinely issued as multiple entry and with a 6 month validity period. That doesnβt necessarily mean you can use it for a completely different purpose / length of stay / number of entries to that stated in your original application. It depends to what extent the change of plan constitutes a material change of circumstances. See Holiday visit to UK with a C-Visit visa which I got for a business trip that never happened; meantime I left the company that backed my application
You could ask the Embassy/Consulate that issued your visa whether your change of plan is acceptable and take evidence of their reply with you to the UK. If you decide to rely solely on a successful landing interview, your best course is always to tell the truth and have paperwork to prove it. Eg if you had leave of absence from your employer for the course, get a new one for vacation purposes. And take your original paperwork with you.