I tried updating my privacy settings and since then I've never heard this ad again. Actually I've started having a variety of ads, instead of lsitening to the same 2 ads all the time.
Might be just coincidence, but could be worth a shot. So here's what I did:
1) Log in to your spotify account (www.spotify.com), and go to `Account`, `Privacy Settings`
2) Tick the 'Facebook data' option. I don't have a facebook account linked to my spotify but it doesn't matter.
3) Untick 'Tailored ads'
Thanks, I changed my privacy settings to not have tailored ads and I haven't heard it once today! Granted I have been off work for 2 weeks so haven't been listening to Spotify as much, but whether this solution worked or the ad just came to the end of its run, I am happy to not be hearing it any more. Thanks for the help!