Landlords are advised to plan up to seven months ahead if they want a successful home improvement project by a quality builder, new research has revealed.

The Federation of Master Builders (FMB) estimates that it takes seven months for an extension, six and a half months for a loft conversion, five months to paint the entire interior, five months for a new bathroom or kitchen, five months to convert part of a master bedroom into an en-suite, five months to convert a cupboard under the stairs into a downstairs toilet and just under five months to remove an internal wall to create an open plan kitchen/diner.

Brian Berry, chief executive of the FMB, said: "A successful building project requires careful planning and our research gives clear guidance to consumers on likely timelines.

"Not only do home owners need to consider how long a project takes to complete, they also need to remember how long they should expect to wait for a quality builder to be available to get going on their project.

"If homeowners want to work with a good builder, they should be expecting to wait at least four months and as a general rule, the larger the project, the longer the wait.

"When looking to appoint a builder, alarm bells should ring if they say they can start next week.

"Experienced and professional building firms are booked up far in advance and it’s always worth waiting for these firms if you want a stress-free experience and a quality finish."

The FMB recommends asking for references from the builder’s previous clients and if possible, speak to them directly about the builder, to always use a written contract and never pay for the whole project up-front.

If a builder is reluctant to use a contract, and demands a disproportionate amount of money up-front, alarm bell should sound, Mr Berry added.

The FMB is now calling on the Government to introduce a licensing scheme for builders so that consumers know that all building firms have a basic level of skill, competence and professionalism and vanquish cowboys.

Richard Truman, head of operations at Simple Landlords Insurance, said: "Factoring in plenty of lead time for contractors to renovate buy-to-let property is vital. It would seem that organisation and planning - as in so many areas - are crucial for investors."