EP: You made a small error in projecting the FV of 5,000 pounds. If you take the interest rate of 4% as "compounded monthly", then you have to project the FV at that rate. If you did that, then the FV of 5,000 pounds =7,454.16.
The FV of the payments is OK, so that the accurate FV of both should be:
7,454.16 + 11,043.74 =18,497.90 pounds.
However, the questioner says the "interest of 4% being applied ANNUALLY", which makes it sound that it is not compounded monthly, but annually. If that is the case, then the interest rate has to be converted from annual compound to monthly compound, which would come to 3.93% copounded monthly. This would only apply to the stream of 75-pound monthly payments. That would change the FV to =11,002.19 + 7,401.22=18,403.41.