There is no difference in taxation in India if you transfer every month or bulk.
If you use specialized remittance services from leading Indian Banks, there would be little difference in fees.
Assuming you are keeping the funds in NRE account in India and hold it in GBP, you get a slight better rate of interest that what you would get in UK. The interest would not be taxable in India, however it would be in UK.
If you convert the funds at hold it in NRE, Rupee account, you would get still better rate of interest. However you are taking the Fx risk when you try and convert this back to GBP incase you decide to stay on.
There are no right or wrong answers
There is no limit on the amount of funds earned as NRE that can be got into India tax free. There is a time limit of 7 Years to get the funds back to India tax free. From a tax point of view if you transfer into NRE account its easy. If you transfer into Normal Savings account you would need some paperwork.