It is actually a standard thing across the country, laid down by central government when it came into force in 1992. it is 10 monthly payments, we even had formula laid down for if someone moved, it is all covered in legislation.
If we swapped someone onto weekly payments it was only 40 weeks not 52 and we had to issue a letter that said that although the person was now on weekly payments if they failed to pay they were still subject to the recovery procedures laid down for monthly payers.
Even the date of 1st of the month is the date everyone should be paying on.
And no, it is an absolute arse trying to collect money in for March. If you don't pay it you then have that payment and the next financial years payment to make, so technically a double payment due in April.
It is all about collecting the money in. And although this sounds harsh it is afterall a government tax that is just collected locally. My advice to anyone struggling to pay it is always contact them (I was lovely and helpful 
)and prioritise them above other debts.
The payments can (and have) been taken directly from people's salary, that is the scary power that they have if payments are continually missed. There is usually no negotiation, it is again, a standard percentage laid down by central government.