Patients with medical emergencies will no longer be able to call at Central Middlesex Hospital from September 10.
The reason for the closure is because fewer patients are using the facilities because the urgent care centre based in the hospital is open 24/7 and sees eight out of the ten patients arriving at its doors-this will remain open.
Patients in need of A&E will now be directed to Northwick Park Hospital's A&E department in Watford Road, Harrow.
The Trust assured that additional resources are being put in place at Northwick Park Hospital to ensure they will be able to cope with the increase of patients.
Chief Executive of the Trust, David McVittie said: "We strongly believe that Central Middlesex will continue to be a thriving local hospital, albeit a different one, looking after our local community for a long time to come.
"Given the reduction in the numbers of patients using the service and the challenges with staffing, we believe consolidating emergency and trauma expertise at Northwick Park Hospital is in the best interests of the most seriously ill patients."
The Trust also revealed that the A&E department at Hammersmith Hospital will close on the same day.
On average, Central Middlesex Hospital have 38 patients per day in the A&E department in comparison to Northwick Park Hospital which have 232 patients per day.
A brand new A&E department at Northwick Park Hospital is due to open in October, already the hospital have opened an extra 46 beds with a further 22 in August, they have also promised to redesign their admissions unit which will allow them to move patients out of the A&E and into a bed much more quickly if they need to see a hospital doctor, this will increase capacity and hopefully lead to shorter waiting times.
The reason for the joint closure of both departments on the same day is due to minimise confusion and for the safety of the public.
As of September people in need of the accident and emergency department will be taken to the nearest appropriate unit which may be Northwick Park, Royal Free, Ealing or St Mary's depending on the nature of the emergency.
On Monday (July 28) a website is being launched which will have more details on the changes, www.nwlondonemergencycare.nhs.uk