Assess the problem. The first thing to check is the outside drains and see if there is a physical obstruction, also seeing that one of your property's drains is visibly blocked will assist you in the further diagnosis. Check all the gutter downpipe drains, simply follow the vertical plastic downpipe running down from your property and inspect the drain, there should be a grille, remove this and have a look to see if there is anything obstructing the drain. Similarly locate the manhole cover for your property and lift this up, you may need a large flat screwdriver to assist. Once this has been lifted check again for anything obstructing the drain.
Gather the right tools. Most of the time simply picking things out of the drain will not solve your issue, you will need some tools. It is recommended to wear protective equipment including gloves and some form of eye protection. Remember you are dealing with waste so must be adequately protected. You will most likely need a drainage rod, available from most local DIY shops. These are great tools that are flexible and will assist in pushing debris through the drainage system. A bucket and hose are also required to flush clean water through the system, and also the bucket will be handy for safely removing any blockages and debris that you may find.
Remove any visible blockages. The most common blockages found in the UK drainage systems are baby wipes, excessive toilet paper and other foreign objects. Make sure you have your protective equipment on and remove any blockages that you can see. You must make sure that as far as you can see, all visible obstructions are removed. This will help in the next step.
Remove any hidden blockages. This is the point that you will need your drainage rod. These tools are fantastic to push blockages along and disperse them to the point where they free up and continue down the drainage route. If you feel pressure on the rod, turn the rod, push it, pull it and move it around to disperse the blockage. Much of the time the agitation of the drainage rod breaks up the offending item and frees it from the pipes.
Clean up around the drains - In order to prevent your drains blocking again, make sure the areas around the drains are clean and clear from debris. Make sure that any drains from the guttering and downpipes have protective grilles on them precenting foreign items from falling into the drainage system. Use a hose or jet wash system to thoroughly clean up around each drain.
If it won't clear - Now that you have followed the first 5 steps, if your drains are still blocked, you will need to call in the professionals. Drains can back up pretty quickly once fully blocked and can cause more of a nuisance in clearing it and with the smells that can quickly appear.