Old enamel bath

Go for vim. I think it will clean it.

Thank you for all the ideas, going to try the biological washing powder first. I had forgotten about astonish, used to use it on my oven, Vim wow that’s a blast from the past, unsure if you can still buy it. I have looked at the enamel diy kits but would have to get someone to do it for me. I had a quote last year for having it done professionally but it was over £800, way out of my budget, loathed to get a new bath it’s such a good size to have a nice relaxing soak in. ?

We had one many years ago and I seem to remember that if it was not worn completely away the best thing was to fill it with very hot water and biological washing powder.
You cannot lose any thing by trying.

I saved up and had ours reenamelled.
It was worth every penny. It cost £300 or thereabouts. It was very worn with black areas under the head and by the plughole. But it's just the right size so I was loathe to buy a new one.

A friend of mine re-enameled her bath herself. She bought a re-enamelling kit. Much cheaper than buying a new bath. I've had a look on line and there are plenty to choose from
Here's one example, www.tubbyuk.com/shop/bath-resurfacing-kits/tubby-standard?gclid=CjwKCAjwtvnbBRA5EiwAcRvnphbrsEzTr0O5Tc2WRIsCOmWQBL3ket-_X9tcnNRWQq02mod9GglR8BoCtPkQAvD_BwE

If the enamel has worn away your pretty much stuffed, I have the same problem with a steel bath but it's not a case of can't afford to replace it, I just want to do the whole bathroom at once. So it's got to wait until we've chosen everything and have the time to do it. It looks horrible but tbh it's only used to shower in these days. I just keep telling myself it will be done soon.

Astonish makes a paste in a rectangular tub for cleaning ovens and enamel bakeware. It’s really good, no nasty fumes and costs about £1. That might work.

I used to use Vim , not sure if you can still buy it