Unblock pipe under sink

Water is getting blocked in the pipe from my house and coming back up and leaking. I thought it was getting stuck in the U-bend but having removed it and checked, it is passing the u-bend and getting to the main pipe (on the left, obscured by the bucket) and getting stuck. Have a video I can****** to show you (cannot add vids to the ad). Given I can use neither the kitchen sink or dishwasher until this is fixed, the sooner you can do it the better.