Will UK Embassy able to find information if i hide information?
It is best not to conceal any information desired in the application form. You may mention the fact about Norway Visa rejected 4 years back and that you are not in possession of the said letter from Norway Embassy. Norway Embassy may oblige you if you have all the details especially the dates and your application references. But it may take time. Meanwhile it is best to apply for UK – disclosing all the facts of your past matters.