No, you only need one quote that covers each measure you are installing.

When you apply for a voucher the Scheme Administrator will compare that quoted price with other quotes on their system to ensure the homeowner is not being overcharged.  The government still recommends you seek out three quotes before making your choice of installers, but, given the very tight deadlines and the limited number of registered installers, it is not a requirement and a single quote is sufficient for this scheme.