Mummytomog, as your circumstances are tricky (self-employed and funding an extension), that is where a broker can come in useful.
In my circumstances (standard remortgage, 2 ft salaried employees with less than 50% LTV), there is no point going through L&C or any broker because all the research I need to do and all the best rates can be found on moneysupermarket.
L&C accepted that in my circumstances, I will pretty much get the best rate of any mortgage provider. How L&C does not suit my needs is because I just wanted them to quote me the lowest rate for fixed, for floating and for offset for 2-5 years, but they insisted on fixing my criteria at the outset (i.e. they will only quote me for a 5y fix), deeming my "needs" to be the cheapest mortgage for a 5y fix. When I asked them to quote me the rate for a 2y fix, they said that I had to make another appointment because my "needs" had changed and so on if I wanted a quote for a 5y tracker ...
Also, in their recommendation, the L&C broker did not inform me what the arrangement fee for that product was. I had to ask them for it. How they explained it what they they added the arrangement fee to the mortgage amount and said it is reflected in the increased monthly instalment. That is slightly misleading because it makes more sense for the arrangement fee to be spread out over the discount period (because most people would remortgage when the discount period ends) rather than over the entire term, which is what L&C were effectively doing.
Fermin, whilst I accept that it is only a small number of mortgage providers such as Yorkshire don't use intermediaries like L&C, that leaves a gaping hole in the market because the best rates for me 2 years ago (when I last looked) and now (remortgage) are still with Yorkshire!