Background check - UK

Hi, 

I've been through a few rounds of interviews with MS and they said they're just waiting for some papers to be signed off and then they'll inform me of the next steps (offer). I was wondering whether I have to list every single job that I've held in the past 3 years, or just the ones that I placed in my CV? 

I asked HR about this and they said that as long as there's no gaps, which there isn't then I won't have to list them. This goes against what most people on wso have been saying. Should I still list them, or omit them entirely - they were only part time jobs which lasted a couple of months. 

Thanks.