Evans Cycles

I work at Evans.
You can do it but it would have to be done via a custom/special order. This takes a while to come in, since it is ordered directly from Brompton, but certainly can be done. The only downside to this is that you would have to leave either a very large deposit on the bike, or buy outright with the vouchers (In either scenario, you are still free to claim a refund as normal).

Best to do it in-store in a store where the staff know what they’re doing. Shouldn’t be too much of a problem, but sometimes a certain member of staff needs to be present to put through such an order.

Also work at Evans - the process for ordering a custom Brompton cannot be done online. The bike cannot be home delivered either, you must collect from the store.
The Bespoke process does take ~6 weeks from ordering.
There should not be an issue with paying on vouchers in-store. You will have to pay the full value up front, and it is non-refundable.

What's your most local store?

Sell the vouchers, order from Compton Cycles local to you who’ll probably deliver in less than a week?

What value are the vouchers, soon to be making a large purchase from Evans, could be interested in swapping them for cash.