In the first instance search SOLO. Many documents are published in electronic form only. Post 2007 search the UK Goverment Web Archive. For current material search the Department for Education pages on GOV.UK or the main publications search portal.
When searching the library catalogue it can be very useful to know the name of the publishing body.
The advanced search option can help limit your results. If you know who has published the item, for example the Department of Children, Schools and Families - in the author field type 'Children, Schools Families' and any appropriate keywords, this will limit your search to that publishing body. This can be particulary helpful with older records, for example 'Ministry Education'.
National Digital Archive of Datasets (an archived site) provides a detailed administrative description