spanish or chinese with business ? careers opportunity?

there seem to be loads of opportunities opening up in China at the moment which is very exciting

That requires knowledge of Chinese? Doubtful. I have a friend who studied Chinese at SOAS then moved to China to work for a multinational. He was the only Westerner on his office floor but everyone spoke English at work. He told me he only ever got to use his Chinese outside of work.

If you don't speak Chinese you'll be more limited in where you can work - for example only international companies in Beijing/ Shanghai. Outside of these two cities, less people speak English and so some Chinese knowledge will be invaluable. Beijing/ Shanghai are the most expensive cities to live in so you could be a lot better off working for a Chinese company in another city in China, for example. Plus, moving to a country without speaking the language also massively limits your travel opportunities, ability to do simple day-to-day tasks like shopping/ accommodation/ bills, etc.

Even if you aren't interested in moving to China and working there (and it's a pretty big decision to make!) Chinese would be very helpful within many businesses, for example trading with China, negotiating with Chinese suppliers, business trips, etc. That being said, Spanish would also be useful within many businesses.

Not really. I know a number of teachers working in China, none of them speak Chinese but they manage to get by easily enough. Sure, if you moved to some provincial city it might be harder - but why would you go there anyway?

I accept that it is better to know Chinese than not you want to live in China, but you are overestimating its usefulness abroad. It is a huge language confined more or less to one country, it is not an international language in the way that French, Russian or even German is. China does virtually all its international business in English.

Supposing that an employer did want to deal with suppliers or arrange a business trip in Chinese rather than in English, you would need to be completely fluent to be of any use, but four years study at university is not enough time to reach fluency. It is also worth considering that there are very many British/Europeans of Chinese descent, many of whom grew up speaking Chinese at home and therefore speak both English and Chinese as a native language - they can and already do fill the (relatively small) number of jobs where knowledge of Chinese is a prerequisite.