That some of the highest mains TDS I've seen, really you need to know what the water pressure is. But I don't believe that any water pressure in the uk is high enough to make 4040 RO systems work at optimum.
Get yourself a decent booster pump any you should get the TDS out below 20
Get 2 resin vessels. Of at least 11 ltr capacity for maximum resin use
Darran