All water tanks will lose heat at a rate that Mitsubishi have measured. For a 170l tank they give a standing loss of 1.63kWh over 24hrs. Which I think is measured from a tank filled at 60°. But that will be a best performance and the tank won't have had heat-conducting copper pipes connected to it when that measurement was done. If I grasp this correctly that rate would equate to the water losing around 8° over those 24 hours. My tank pipework was not lagged initially and it was noticeable how warm it made the space it was installed into, and how hot some of those pipes felt. Even the hot water loop that circulates through the heat exchanger would still feel hot several hours after a cycle suggesting to me that the water in the loop was passively circulating from within the tank as it cooled in the pipe. It is damned fiddly trying to insulate the tank pipework as it is all bends and valves and pumps but you are reducing heat loss from the one part that you are trying to keep really warm 24/7/365.

Thats ample enough h/w for 2 showers and the washing up.

My upcoming service will be carried out by a contractor from the Housing association not Mitubushi unfortunately so I’m unsure how knowledgeable they’ll be with advice on the settings.
My COP over the last 2yrs is only 2.4. 
Iv recently changed my setting from adaptive room to curve although we’ve not really used the heating side since the change of setting.

Based on mine, I suspect your losses from the HW tank are as expected.  It's not going to cost much; mine costs less than 2kWh per day to maintain temperature even if I don't use any.

Is that your heating COP or overall?  

I moved to auto adapt last winter and found COP went down but overall consumption was the same or a little less.  With AA you need to be careful if you vary your room temp because AA bumps the flow up quite high when heating up to a target room temperature. 

Thats ample enough h/w for 2 showers and the washing up.

My upcoming service will be carried out by a contractor from the Housing association not Mitubushi unfortunately so I’m unsure how knowledgeable they’ll be with advice on the settings.
My COP over the last 2yrs is only 2.4. 
Iv recently changed my setting from adaptive room to curve although we’ve not really used the heating side since the change of setting.

It will lose heat through the tank insulation as well as the pipes.  The pipes will make a small but significant difference.  Your tank is smaller than my 250l one so the pipes, etc., will have a bigger effect. If you're really interested in HW tank heat loss then have a look at this. 

https://www.aivc.org/sites/default/files/airbase_7801.pdf

Also, what is your HW temperature?  The hotter it is, the faster the tank will lose energy. A 55 deg tank will emit more heat (i.e. lose energy faster) than a 45 deg one. 

Let us know what the engineer says. 

pipes arnt lagged that feed off the tank which I’d imagine they should be although I’d of thought that reason alone wouldn’t amount to 1 degree an hour??

one issue I’m having is that my hot water loses very close to 1 degree an hr throughout the day.

I do have an annual service in a few weeks so I’ll mention it.

Mine loses about 0.6 degrees per hour so a bit less.  Is your HW tank outside the house, e.g in the garage? That would make it lose a bit more than in the house.

one issue I’m having is that my hot water loses very close to 1 degree an hr throughout the day.

I do have an annual service in a few weeks so I’ll mention it.

I think you are suffering from the same problem described above; Melcloud over estimating consumed energy when the heating is off. 

At the moment the heating is turned down to 10c with the hot water on a timer to come on for only 2 hrs a day on a low/night rate between 5 and 7am.

Below are images that shot the heat pumps usage. 
As an above post, has to be reading incorrectly??

I also now have a really good idea of winter running usage - it's working really well. Our whole house electricity use has been just under 13kWh a day Nov-April, the delivered heat and direct heatpump usage is approx 1/3 of that predicted by the heatloss survey. The house is average 18.5 degrees. All things considered, apart from the dodgy readings it has been a thoroughly pleasant experience. My neighbours are so impressed that they're looking at installing one!