Ask your GP for a referral to an ENT... I'm Canadian. we have a similar medical system.

A couple of points to note... a base of tongue lump you cannot see as your tongue is very long and it's base is inside your throat. If you can see it it's on your oral tongue and by the sounds of it is under near the back/side. Why I am making this point is that base of tongue cancer generally has a different cause (often - though not always - it's HPV related)

Oral tongue cancer can be caused by heavy smoking and / or drinking. Since you a smoker (take this as motivation to quit - even if it's not cancer - which it probably isn't) - Other people just get it - that's me - just look at my signature though I do have a theory.

Also tongue cancer can be painless. Though the deeper it is the more painful it gets - as you know if you've had ulcerations.

Mine started out as just a reddened area and it was painful and inflamed - but underneath was a lump. There was no broken skin just a lump.

You do not want to see a dentist if you know of a preexisting issue, they do dentist stuff, and can tell you if there is a problem (since they should do oral screenings ) but they cannot treat you or biopsy you so you are wasting time at this point. They can refer you to an Oral surgeon who can do a biopsy, but if it comes back as cancer you will need to see an ENT (a good one who deals with oral cancers) All of this referral process takes time. SO best to ask your GP for a referral to an ENT right off the bat, and then once you have a date if it is too long off push to be put on a waiting list.

In the mean time if it is an ulcer it should heal. ;o) If it progresses and becomes painful, ask your GP for a prescription of oracort. If I have a sensitive area that flares up - I step up my cleanings and rinse my mouth after I eat then apply some oracort to the affected and usually in a day or two I'm back to normal.

best of luck.