Limescale buildup

You could install a scale reducer on your cold. I believe there are some sort of tablets that you can put in your cistern to reduce scale build up also. There is also a chemical bleach called harpic in a black bottle available from most supermarkets. This could sort it if you leave it over night and then just use it regularly to prevent further build up.

The limescale build-up is unlikely to be related to the recent emergency plumbing work, especially if it was already an ongoing issue before the toilet blockage and seal replacement. Limescale forms from hard water minerals and tends to accumulate in areas where water sits or trickles continuously. If Spirit of Salts has previously removed it but is no longer effective, it may be that the deposits have become much thicker and harder over time, or there could be limescale build-up extending inside the rim channels where the cleaner cannot easily reach. Another possibility is a small, continuous trickle of water into the bowl from the cistern, which can accelerate limescale formation. This would be worth checking if you notice water constantly running into the pan. Based on the information provided, it does not immediately suggest that the recent repair was carried out incorrectly. However, if the problem has become noticeably worse since the work was completed, it may be worth asking the plumber to inspect the toilet flushing system and confirm there are no leaks or continuous water flow issues. A few photos of the bowl and the affected area would help determine whether this is simply heavy limescale build-up or if there may be an underlying issue contributing to it.