Potential Contaminated Land

ConLandProf

You can find out the available information about the site your house is on via services like Landmark or Groundsure..  You will need to pay for their reports.  As other respondents have mentioned the local authority will have the planning documents on its planning portal and any conditions related to it.  However, this may be hard to find if you do not have the historic name for the area that was redeveloped.  Your local authority should have a "contaminated land officer" who should be familiar with the site history and ought to help you find the information you seek.   Be aware that some remediation work can be limited in its effectiveness, as may be the input of the environmental regulator, so question the CLO closely.  (I tried to give you the links but the site blocked me).

If you take an insurance route take care to ensure the cover does not have exclusions for land contamination.  Many policies do. 

If you are having difficulty getting the help you need, then you might want to consider contacting a local councillor to complain.  

I personally would not buy the house if the vendor is unable to give you a coherent response about its land condition.  Without good information you are at risk both of your house losing value and of taking on a remediation liability (if further work is needed) as you would become a "site owner" under the "Part 2A" legislation.