The answer is no! Your landlord cannot ask you to pay more ground rent than it is stipulated on the lease. The ground rent is usually a fixed amount that is written down on the lease and you are required to pay just the amount that is written on the lease.
But there are some leases that have a clause that makes it possible for the ground rent to be increased after a number of years in order to combat inflation. In the older leases this time used to be, 33 years and you were supposed to pay a fixed amount of money and that money could only be increased after 33 years. For example if you start lease with an amount of 70 pounds per year, after 33 years you will be required to pay 140 pounds per year. It is not a must the ground rent will double after the 33 years, it usually depend on the formula you will use to calculate the increase of the ground rent. Alternatively, any increase on the ground rent can be calculated in accordance with a published and recognizable formula.
Having said that, you should be very careful when it comes to purchasing newer leasehold homes. Some developers are inserting a clause on the lease that allows them to double the ground rent after each and every 10 years. This means that if you are paying a ground rent of 150 pounds per year, you will be required to pay 300 after 10 years, 600 after 20 years, 1200 after 30 years, so you can imagine the amount for money you will be required to pay after 100 years. The government is working on how to stop this but in the meantime you can avoid being a victim of ground rent scandal by using the help of a solicitor when you are buying a leasehold property.