Mr Arulampalam is already talking to colleagues on the phone as he arrives for work at 7.45am on Sunday.
During a 20-minute handover, when he finds out about the most seriously ill patients under his care, he has to contend with the arrival of a "code red" patient who needs immediate treatment in the "resus" area of Emergency.
He quickly delegates that job to a senior doctor, asking to be kept informed on the patient's progress, and starts his ward rounds.
It's his first big decision of the day - many more will follow, because there's a lot to do.
Mr Arulampalam is in charge of all patients admitted for general surgery at the hospital this weekend.
His role also involves reviewing patients who have already been admitted during the last few days, who have had surgery and whose care is ongoing.
He must also supervise operations, particularly those involving junior staff, and talk to the families of patients who are seriously ill, especially those who have a high risk of dying during surgery.
Weekends start on a Friday morning at 8am and finish at the same time on a Monday.
Although he is contracted to work just three hours on each of Friday, Saturday and Sunday, Mr Arulampalam usually only goes home at night to sleep.
He also has to be on the end of a phone in case he is called back in for an emergency.
"On a weekend, my family don't expect to see me," he says.
Such is the workload over the period that he often swaps one day with a colleague because "doing a three-day weekend is not safe", he says.
First on his ward round is patient Nancy Fuller, who was admitted on Thursday evening with a painful wound after surgery.
She says she has no complaints about the weekend care she has received.
"I wasn't feeling too good this morning and they immediately did something about it and got medication for me," she says.
An hour into his shift, Mr Arulampalam has spoken to the consultant gastroenterologist about an emergency operation, chatted to the orthopaedic surgeon who's preparing to fix fractures and is under pressure to book a CT scan, which will mean liaising with the consultant radiologist.
Among senior doctors, he says the staffing levels are "really very good" at the hospital outside of normal hours and that helps when difficult decisions on patients have to be made.
Meanwhile, the "code red" patient brought in from a residential home with bleeding needs more tests in a hurry.
This requires more conversations with specialists - asking for their advice and sharing knowledge.
"Communication is really, really important," he says.
At 10am Mr Arulampalam has seen about half of the patients on the emergency ward and he's stacking up work for the rest of the day with two patients already needing to go to theatre.
Sometimes he can get away early, but not today.
With a house officer, a core trainee, two junior doctors and a registrar working with him, it only takes two or three of them to be called into theatre and the most junior person is left with responsibility for all the patients.
"So I'm in most of the time. And, you know, it's a huge benefit for the patient if they've got someone doing the strategy and making sure that things get done. Basically mopping up and planning for the next 12 hours."
Heather Cannock is next on Mr Arulampalam's list. She was admitted on Thursday to have a procedure which relieves severe pain in her bowel and says it's reassuring to have a consultant like him there at the weekend.
"You know they're there and you've not got to wait the whole weekend before you see someone," she says. "I know the nurses and the junior doctors are absolutely wonderful but having a consultant is definitely better."
It's 1.30pm and Mr Arulampalam is in the surgical admittance ward with nurses and junior doctors looking at notes on patients including Nicola Betchley, who needs her appendix removed.
Her mum took her to a walk-in centre first before they were quickly directed to the hospital and things have moved fast since she was admitted, to the extent that she is having an operation that same afternoon.
Nicola says her care has been "really quick and efficient" but her mum would like to see GPs working seven days a week, because that would have been her first port of call.
"I don't believe in going to hospital unnecessarily. I think GPs should be available," she says.
Six hours into his shift and Mr Arulampalam still has 10 emergency patients to see on his ward round. Two emergency operations have been lined up and a third now also needs to be done while two CT scans have to be reviewed and acted upon as well.
"So we'll be operating well into the evening," he admits.
In his personal opinion, is it feasible to run a seven-day NHS - where operations are planned, clinics run and tests carried out just like every other day of the week?
Mr Arulampalam is very sceptical.
"There is a seven-day emergency NHS and it's just about staffed to run safely.
"But I don't think consultants should be doing non-emergency work seven days a week without a greater debate about what we're trying to achieve.
"Because a consultant on their own will achieve nothing without phlebotomists, radiologists, radiographers and all the other staff needed to support them."
At 9.30pm, our consultant finally gets home, but not before saving the patient in resus by getting the radiologist to stop bleeding from a major blood vessel.
"One appendix left to do and all emergencies seen. I am knackered, as are the team!"
Tan Arulampalam, consultant colorectal and general surgeon, let the BBC follow him on a weekend shift at Colchester General Hospital, where he's been a consultant for 12 years - and he gives his personal view on the plan to make the NHS a seven-day operation.