Modern cars do tend to use a little more oil, for petrol at least the engine oils are thinner than they used to be, low friction piston rings and wet belts all contribute to oil usage.
That said, the car should have sufficient capacity to last as per service manual recommendations even though in recent years this guidance has caused a lot of engine failures due to the use of wet belt engines and extended service intervals.
If you are averaging only 7000 miles then the option for Diesel compared to Petrol is not strong, also make sure you are checking your cars engine oil on a level area, not on a slope etc. a service may have topped up your engine oil level but an MoT will not 
In a completely sane world, madness is the only freedom (J.G.Ballard).
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