UK ETA with a 10-year-old suspended sentence (Expunged in Spain) - Need advice

I have a trip to the UK booked with friends for this summer. We booked it months ago, but I just realized that a stupid mistake I made when I was 18 might get me denied at the border.

It happened 10 years ago: I committed a robbery offense, was arrested, and received a 2-year suspended sentence (no actual prison time). Those criminal records are now legally expunged/cancelled in my home country (Spain).

My questions regarding the ETA application are:

• Do I have to answer 'Yes' to the conviction question, even though I didn't go to prison and the sentence was suspended?
• If I answer 'No' (because I wasn't in prison and my record is legally clean here), will I be able to enter, or does UK Border Force have access to my old arrest records anyway?

Thanks in advance for your help