There are products but none seemed to meet our requirements. So I looked at the marine industry and found the Italian Soliban panels - very thin, very efficient and have no junction boxes etc to increase the profile height of the paenl . . . but you don't have to speak Italian to translate "molto costoso".
Fortunately, in the course of speaking with our builder - John, he mentioned that the electrical wholesale dealer that supplies a lot of his accessories, also sells the Voltech brand of solar panel. Comparison of the Solbian and Voltech panels indicated that they were very similar in specification although the Voltech panel had we were told a 10mm high junction box sitting on the end of each panel. Maybe we can get around that and you don't have to speak Italian to understand that compared with the Solbian panels the Voltech are "molto più economico".
With the Voltech panels - which we are guessing are from India? - we could fit 6x100 watt panels on the roof and . . . I can go back to speaking English.