Your post doesn't make clear whether you are describing the old conditions that you used to work in, pre-Covid, or the conditions that you anticipate working in once you return.
Most of the offices and work environments I have heard of seem to be implementing all sorts of measures, as specified by government guidance - such as screens, one way systems, reducing the number of people in at any one time, and so on. Many employers are finding that they simply cannot fit the full number of workers into the existing office space, and are expecting large numbers of staff to continue working from home for the foreseeable.
I suggest you contact your employer and find out how they are implementing the government guidance on social distancing at work, and what measures they are taking. If they are not following government guidance, then you may be entitled to wear a mask, and ask for a risk assessment. Obviously, different jobs and work situations will vary, but you can find the govt guidance for your type of job on the
www.gov.uk website, so that you know what to expect.
Regarding your point about sanitising. To be honest, I would be MUCH happier doing it myself, rather than leaving it to someone else. At least then I would know it had been done properly.