do I have to create another business on top of the first one (I'd rather not)?

Hi, I'm a freelance journalist who registered as sole trader. When I registered to HMRC - and created my business -I described it as 'media and journalism'. I tried to remain quite broad as I wasn't too sure what different activities - always linked to the communication sector though - I could include. Today a small company would like me to help it translate its website from English into French (my mother tongue), rewriting that a bit. I would like to do it and would naturally invoice them and declare it to HMRC, there's no problem with that, right? And for the invoice, could I put this activity under the business ('journalism and communication') I already have (because I write stories in French about things that are hapenning in the UK, I already translate and write a lot) or do I have no other choice but to create another one (I'd rather not to be honest), more focused on translation only (but to be honest, this translation job could be a one-time thing)? To avoid creating a new business, could I in exchange modify - if needed - the description of my company into something more precise such as "journalism, communication, translation, photography" intead of "media adn journalism"? Many thanks,

Hi,
A single UTR is all that is required for multiple trades.
Set up as self-employed (a 'sole trader'): step by step
As you will have more that one busines running side by side, you will need to keep separate accounts for each business.
When completing you Self Assessment tax return, you will declare the gross turnover and expenses for each business separately, with each business declared on its own individual SA103 supplementary page.
If your combined gross turnover from all your business ventures exceeds £85000, then you may need to register for a VAT account.  
Have a look at the guidance here:
Register for VAT
Thank you.