The government website, as mentioned by the PM last night, has full details of what we all can and can't do:
Here's the relevant part to answer your question:
Going to work
You may only leave your home for work if you cannot reasonably work from home.Where people cannot work from home - including, but not limited to, people who work in critical national infrastructure, construction, or manufacturing - they should continue to travel to their workplace. This is essential to keeping the country operating and supporting sectors and employers.Public sector employees working in essential services, including childcare or education, should continue to go into work.Where it is necessary for you to work in other people’s homes - for example, for nannies, cleaners or tradespeople - you can do so. Otherwise, you should avoid meeting for work in a private home or garden, where COVID-19 Secure measures may not be in place.