I reported a health and safety issue at work and it wasn't taken seriously. What do I need to do next?

This will really depend on the company you work for,

Are you in a union? if so, bring it up with them , but as Pogo said, you could be classed as a troublemaker,and they could threaten you with the sack.

But if this is not being taken seriously, you will have to take it to the HSE..

but do make a note of everything,for any future contact with the HSE,or your bosses.

otherwise keep this low key,don't dig yourself a hole to fall in

Report it again, and perhaps encourage other colleagues to support your concerns.

If the complaint is 'serious' and no appropriate action is taken, then then report to the Health and Safety Executive.

Nothing apart from asking for a written acknowledgement of your concerns if it was a serious issue. I wouldn't make too much out of it as they may see you as a troublemaker. If it is a serious H&S issue, report it to the H&S executive.

Report that the report was not taken seriously

Report it directly to your manager in writing. If they give you any grief about it, tell them that it is a legal requirement and you would be breaking the law if you didn't (which is true btw.) If I were you I'd email the report, that way you have a copy and evidence of sending it.

If you're a member of a union, it might be worth mentioning it to your union rep too, just to keep them in the picture.

Nothing...If someone gets hurt they will be to blame.

If the issue is that serious that serious injury is likely to happen then report it direct to the HSE.

Contact HSE maybe

Leave.