But if you are confident that your skill/ ability can take you beyond your current band/ role, or to another company if needs must, then I would not let it concern you in the slightest.
Also 5 years is a hell of a long time, much will change. Hell I started work 6 years ago. From where I was then to now is chalk and cheese.
Lets go a bit further in trying to explain this.
Company A and Company B have exactly the same pay scale today, and two exactly the same people join in each and in 5 years time rise up 1 pay grade each year.
Today - both employees start at 20K today and every year they both go up one pay grade.
Company A
20K - 21K - 22K - 23K - 24K -25K
Company B
20K - 21K - 22K - 23K - 24K -25K
5 Years Time - both end up on the top tier of pay for their role, but the public sector worker will get nearly £2K less then if they had started work in the private sector
Company A - Capped at 1% rise each year
21K - 22.1K - 23.1K - 24.1K - 25.2K -26.3K
Company B - Lets just say 2.5% each year
22.6K - 23.7K - 24.9K - 26K - 27.1K -28.3K
As it has been mentioned, I could move away to look for work elsewhere in a few years time but the issue still remains. With private sector jobs already paying more, this will only widen the gap in similar roles, and squeezing the gap between the public sector and MW.