That's odd Crampton. You should be able to register even though you're not making a claim for JSA.
There are two types of JSA
The first is contribution-based Jobseeker’s Allowance and this is for people who have been working for at least two years and have paid enough National Insurance to qualify. This type of benefit is paid for a maximum 182 days.
The second type is income-based Jobseeker’s Allowance and this is based on your income and savings. If you have savings over £16,000, you can’t usually get it. However, it’s still worth applying as you may be entitled to SOME money…