The Honda ev6010 has two 120v outputs, with a center tap neutral connected to ground. Searching the internet many seem to suggest connecting a load across the two 120v live wires to get a combined 240v however I get 0v on a multimeter when I try this.

That's because you only have a 120 V feed. In a house you have 2 separate 120V feeds. You could try a step up transformer. What are you trying to run and what is the Wattage of the generator?

I assumed the two outputs from this generator are alos separate 120v feeds. Each one appears to originate from a separate coil on the stater and each one has a separate switch. I'm wanting to get 240v as I live in the UK and a 120v ouput has very limited use to me.

If you only have 120V outlets, the generator is wired for 120V. Regardlaess of how the wires are placed, you will only get 120V. You will need a 240V generator or a step up transformer.

The EV6010 uses two separate 120v outputs. These are normally wired in phase so they can be run in parallel for full current at 120v. Because of this if you measure between them you will see 0 volts. For 220v all you have to do is rewire to place the outputs in series. This is covered on page 23 of the Honda install manual.