Hi, you could invest the £10k into a one year FRB, for example Birmingham Midshires 5.50% AER. Remember no withdrawals are permitted during term of the bond, you are able to make additional deposits as long as the bond is open to new investors, when the bond is closed to new investors then no additional deposit will be accepted.
Also you could open an easy access savings account, such as the ICICI HiSave account at 5.15% AER, to invest the £750 per month, this would give you the option to withdraw your savings if/when you require with short notice.
The tax free option would be a mini cash ISA, however the maximum investment in a mini cash ISA is £3,000 in one tax year, and only one mini cash ISA permitted in each tax year.