First of all an incomplete garage wouldn't stop Bovis forcing you to legally complete for their financial year end. My guess is, having missed their half-year on 30 June The original completion date, urgency and momentum on site slowed. The reason you cannot legally complete is because your new home is nowhere near finished and Bovis, being incapable of forecasting 6 o'clock at half past five, are unable to give you an accurate date even now! Yes within reason completion dates are estimates or forecasts, but Bovis have been 8 weeks out since roof completed. The home could have easily been finished in that time and there are no weather delays once the roof is on, so their "estimate" should be accurate!
You are quite correct, Bovis have and continue to breach the Consumer Code for Home Builders Requirement 3.2. At roof they should give you the MONTH the home will be finished and ready for you to move in. They did, although they are (at the moment) two months out!
So you can get compensation using the Consumer Code. The maximum is £250 for "inconvenience" which is a slam-dunk. You should also insist that the £120 registration fee is also refunded (otherwise what is the point!)
As for anything else, you will have to prove with receipts, why you are out of pocket.
This could be, rearranging a mortgage, valuation and fees. Additional legal fees, extending your rental agreement (but not for rent, you would have to pay a mortgage if the home had been ready on time), any rent you may have to pay for any term left on your rental lease.
Do please have your home professionally inspected and snagged.
(I always recommend Tim Fee of Snagging Inspections.co.uk 07768 900200)
Bovis are one of the worse housebuilders, especially after you have moved in and report defects.
Do not legally complete on the home unless you are 100% happy and satisfied everything is as you want it.