Have you referred it to Environmental Health? Complained to Thames Water?
You should make a formal complaint in writing to Thames Water. You also need to speak to the Environmental Health Department at the local authority because clearly, this is a health hazard.
If you have to close your office, you are entitled to claim compensation which would be the cost of relocation if you have no alternative but to relocate. With regard to loss of profit, you are entitled to compensation but I have experience of putting the claims together and it really needs a forensic accountant to put the evidence together otherwise the claim will fail.
Here is an article on just this subject from a different area.
Can I clarify anything else for you?
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