Affiliate Marketing Secrets

Please could I have some advice on the UK’s video creation and sharing laws.
Is a website allowed to share or even sell a users uploaded video content if it is a part of their Terms and Conditions which have to be read and ticket before every upload. Also the video content being uploaded by the user was produced by that person or that person has the right/ been given permission to use the content upon which is being uploaded.
The sites T&C’s are along the lines of :
By agreeing to the terms and conditions, Users acknowledge and accept that the site has the right to use a user uploaded content.
By a user agreeing to the terms and conditions, Users acknowledge and accept that the site may use uploaded user video content across their own site and affiliated social platforms.
By agreeing to the terms and conditions, Users acknowledge and accept that uploaded user content may be provided to affiliated third party companies. User understand third party companies have the right to use this content for the purpose of consumer research and have the right to displaying this content on on their own website site and other affiliated websites.
By agreeing to the terms and conditions, Users acknowledge and accept that the site has the right to use and edit uploaded user content. User content will be edited by adding a small watermark company logo at the bottom right side of the video clip and will display throughout the duration of the video.
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If anyone can recommend a firm or even person that specialises in UK Video Law please post a link or contact info.
Really appreciate any help!