Hello Georgem1994,
Good advice from our very experienced Members.
As Member Centralheatking stated the Washing machine standpipe is definitely too short - it needs to be extended to as high up in the Sink unit as possible with just enough gap under the Sink to hook the Washing Machine waste hose into the top of it.
The standpipe should also have a couple of pipe clips to hold it firm to the side of the Sink unit so that the Washing Machine waste hose does not pull on it causing leaks at the trap.
Before You extend it with a piece of waste pipe you should take Member ShaunCorbs advice and check that the existing waste pipe / trap is not partially blocked.
I would try cold water first and if the water does not run away as quickly as you would expect disconnect the trap and have a look at both the trap and the waste pipe that it discharges into.
Extending the existing Washing Machine / Condensing Boiler condensate pipe [?] waste pipe to as high as possible within the Sink unit should solve the problem - but if it does not You would need to fit a Washing Machine trap to the Sink waste fitting - this replaces the existing Sink trap and has a spigot where the Washing Machine waste hose connects to and is secured with a Jubilee clip.
You would probably have to slightly alter the Sink waste pipe to suit a new / different trap.
This is a good quality Washing machine trap:
• 75mm water seal• Includes a WMF3 nozzle• Can accept discharge from a washing machine or dishwasher• Manufactured in polypropylene• Conforms to EN 274-1:2002
www.toolstation.com
Good Luck in resolving the problem.
Chris