If the woodland is to be purchased using a mortgage, I'd hazard a guess that the provider will require the 'extra' to ensure that the land is safe from future development which may reduce the value of the land and therefore put their money at risk (notwithstanding that development may also increase the value!!).
If financing by other means, the searches should be at your discretion and possibly could be viewed as due diligence. The solicitor may be covering his/her back by suggesting the additional search.
If it helps, info on searches can be found here:
http://www.envirocheck.co.uk/products/e ... ck_report/