[mrs bouquet]

Ongoing conversation with a UK lawn specialist about Speedwell, has come up with this.

Benefin.   N-Butyl-N-ethyl-a,a,a,trifluoro-2,6-dinitro-p-toluidine (56)

I cannot find any reference to this in UK or connect it to a product we know.   Please can you help.  Mrs Bouquet

[Pescador]

https://www.solutionsstores.com/benefin

This gives some information, but be aware it is an American site so the legality of use in UK may be different.
It doesn't look as though it would control existing speedwell, but should prevent any seeds germinating to form new plants.

[mrs bouquet]

Thanks for your reply.  I wondered if it was a US only product, due to lack of UK info.    Ah well, I tried  Mrs Bouquet