The rules for those embarking on the popular London-to-country move have changed, says Philip James of Strutt & Parker.

The migration of property owners from London to the country is a long-established phenomenon, particularly for growing families who want a slice of the rural lifestyle.

This urge to move is an influential factor in the market and is a hugely important factor in keeping London and country sales ticking over.

As families expand, demand for space increases and children prepare to move school. City dwellers start their calculations - for example, how much they can get for their money against the length of a commute. Some will have a specific destination in mind. Others will need expert guidance on which areas fulfil their important criteria.

But while this traditional exodus has traditionally underpinned the country property market, particularly in Kent, the rules have now changed in one important respect.

Thanks to the current disparity between the quick-fire London market and the more hesitant out-of-London scene, London buyers in a good property are now considered by sellers in the countryside as a good prospect - and are securing exclusivity deals - even before instructing an agent on their own sale.

Provided their own home is a good prospect, the speed at which transactions are being done in London means that they can be considered proceedable. Many sales are now being started on this basis.

For vendors in the country considering accepting offers of this kind, it is essential to be with an agent who properly understands a buyer's situation. It can be the difference between a good sale and "the one that got away".

Recently Strutt & Parker has put together a number of deals of this kind, in some cases ultimately handling both ends of the transaction. Our country negotiators often have many years' experience in London, and vice versa.

Along familiar migration routes - for example from Fulham to south east Kent - we will have a detailed grasp of which areas London buyers will want to look at, and whether where they are selling is likely to perform well and quickly. By encouraging the right London buyers to make offers, we can start the ball rolling where it would not otherwise have done.

A London buyer still waiting to instruct may in some cases be an even better bet than a cash buyer sitting in rental property, who is more likely to be playing the field. London buyers who put their house on the market on the strength of wanting something they have seen are extremely likely to remain committed to that deal.

This is particularly true now that Londoners who used to take more than one step on the ladder before arriving at their long-term family home are now looking to achieve it straight from London, to avoid multiple stamp duty costs.

An estate agent with a strong presence in London and a comprehensive country network will be in a much better position to fashion a deal in which both buyers and sellers have confidence. In today's unpredictable market, it is an essential talent.