Please don't leave this. As stayathomegardener says, you need to urgently rule out cancer, especially with a smoking history.
If you're worried you can't get to see a dentist, go back to your GP on Monday, ideally a different doctor.
If you're worried about being fobbed off, go armed with the NICE cancer guidelines. These are national guidelines for all medical practitioners. These are for England, I'm not sure how to get the ones for Wales but for suspected cancer they will be the same.
Scroll done to the bottom of page 29 of the guidelines.
www.nice.org.uk/guidance/csg6/resources/improving-outcomes-in-head-and-neck-cancers-update-pdf-773377597
It's difficult to see clearly from your photos on my phone but these are the criteria for urgent referral (to be seen within 2 weeks) and certainly one of them will apply to you:
"Urgent referral guidelines (England)
• Ulceration of oral mucosa persisting for more than three weeks.
• Oral swellings persisting for more than three weeks.
• All red or red and white patches of the oral mucosa."
Insist on being referred and show them this as evidence of why. The GP or nurse can't deny it is needed then.
It could be nothing but it certainly needs looking into further. Good luck and please don't allow them to put you off any more.