Yep, that's where the washing machine drain connected to.....either block the hole up with something (cork, silicone) or you can buy connectors which have the end blanked.
John
And while you are at it, buy and fit a blanking caps to to the open ends of the valves with blue and red handles respectively, e.g. Screwfix 39553. If either valve gets knocked, you will have a flood.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local