buying a 2nd car i.e. diesel runabout will never cost in !!
best case it will be £2k a year cheaper on fuel...from this saving you need to take away
insurance - £400 ??
tax - £120

deprecation - £2k

maintenance - £1k ??
griminess of driving a diesel oil burner when you have a GTI at home - priceless

put the miles on the GTI (you are being paid to do it) or sell it and buy a run about ...dont keep both ....