Car dilemma

The other day at work i found out that i won’t be getting a company car in the new year, the reasons are fair so i am not holding a grugde about it even though this one of the reasons i took the job.  But the demand for the on site work has not grown as they had planned so i have no reason to have my company car, but i get use of the pool car for the days that i need it.  My daily commute is just over 30 miles a day on small A roads. I currently have a petrol BMW 320i, so the it drinking the petrol.  So in the new year i plan to buy a diesel. With having own diesel i could use it for work when required and get paid per the mile etc.  I spoke to one of the sales guys in my place, as this is what he does and he runs it like his business and makes a bit of money using his own car.  So if the on site work did grow in the near future it is possible i could earn a bit more cash.
 
But here is the issue, i don’t have the free cash at hand to buy the sort of newer diesel.  So my choice is to buy a older diesel with high mileage with the cash i have.  Something like a Volvo S60 D5 or Honda Accord or a older VW passat all with over 100k + on the clock?  Most like would need replacing 3-5 years later.  Or do i get a newer car say a 3 year old and get the car on finance what i can afford to do.  Something like Mazda6 or the newer accord or the new style passat.   With around 50-70K on the clock?

I have sometime to make up my mind, but was just wondering what others think about it and what they would do.

Have you checked the company fleet manager to see if they get a discount with any of the lease companies? They might be able to get you a really good private lease deal with the same fleet company they would have used for your company car.

Given the depreciation rate of car value, leasing doesnt seem a bad idea. I'm surprised more dont do it