Pretty sure it's not just a British term. This American dictionary gives mostly the same meaning. Slop: thin tasteless drink or liquid food https://www.merria

Pretty sure it's not just a British term. This American dictionary gives mostly the same meaning. Slop: thin tasteless drink or liquid food https://www.merriam-webster.com/dictionary/slop https://www.merriam-webster.com/dictionary/slop