Laying new turf - remove existing lawn or rotavate in?

[Townorcountrysideliving]

So we're returfing the lawn. Half of the existing lawn is still there and it's quite weedy and mossy. We've short listed some companies to do it. The cheaper one (still expensive!) proposes to use weed killer beforehand to get rid of weeds. Then they will rotavate the existing lawn into the ground before applying top soil, levelling etc. Another company (a lot more expensive) propose to remove the existing turf, including weeds, entirely before applying top soil etc.

Is there a "right" way to do this? Or are both methods equally effective? The company rotavating the existing turf into the soil says it makes no difference as long as we have applied weed killer two weeks before they start.

We're happy to pay more if removing existing turf is the right way to go!

I would get the old turf and weeds removed. The weed killer might leave your soil in poor condition, and is a bit overkill really. Once you remove the weeds, they won't come back.

@rosiedeus thanks. This will be the option we'll go for.