Replacing lead mains pipe-flush system?

[bootsyjam]

Have bought an old house and had water samples taken by water company and they're MASSIVELY high for lead content so are getting the old lead mains pipe replaced.
Pipework in the property is ok and we're getting a new water tank to be as safe as we can be.
Does anyone know if there is some sort of chemical flush/clean that we can put through the existing pipes? Our plumber was going to research it as he wasn't aware of any, was wondering if anyone here had something done/had heard of anything?
Any advice/info gratefully received.

You won't need to flush the pipe with any product because the lead will no longer be there. When the water company reconnect your supply at the external stop tap they should check the company service pipe (the branch of pipework their side of the stop tap out to the main under the road) and replace that if it's lead. The only thing you should need to do is run the tap for about 30 minutes to remove air or sediment from the supply.
You should only be using your kitchen cold tap as a drinking water source as that's the first first tap off the rising main .
If you have a header tank (usually in the loft) it's usually open topped and is effectively stored water, which means the chlorine evaporates off and nasties can get in. So don't drink from the other taps.

Brilliant that's very helpful, thanks very much!
The piping company is also installing the company service pipe as they're fully Watersafe accredited but it makes a lot of sense to pay VERY close attention to what they're doing at that particular section!

https://www.dwi.gov.uk/lead-in-drinking-water/#:~:text=Those%20at%20particular%20risk%20are,kidney%2C%20heart%20and%20circulatory%20health.
Get rid of all lead pipes.