Companies House is the registration point for all companies in the UK: http://www.companieshouse.gov.uk/

The register is publicly searchable here: http://wck2.companieshouse.gov.uk//wcframe?name=accessCompanyInfo or you can use third party sites like Duedil: https://www.duedil.com/ which tend to collate information from multiple sources and so may provide you with a more detailed picture.