I cannot really give a fair review of this as my mind was preoccupied at the time, but I have used this restaurant before. It is not as small as you think it is. There's the seating area by which you enter which is in the form of a conservatory/marque. Then an indoor seating area opposite the kitchens and service space; but, venture further and there is a small, brightly lit room at the back offering plenty of seating since no one seems to know it is there. Particularly useful for access if the entrance is full.
I only had a cup of tea here and it was perfectly acceptable although served in a slightly too utilitarian style. I had the aluminium-tea-pot-and-plain-white-crock-cup-and-saucer combo that, while serviceable, I always think of as not very National Trust. Still, at that time, my mood was such that I soon abandoned the place to roam the gardens in the lamping rain trying my best to get thoroughly soaked, switching off the oxygen to exacerbate the maudlin feelings, hoping to align myself with that most Romantic of fates, the onset of a fatal, consumptive cough. Think Wollstonecraft on Putney Bridge, Keats on top of a coach in a pelting rainstorm, Byron in the swamps at Missolonghi.
Which did not work. Back outside the restaurant, an elderly lady asked me if I was alright. Which ruined the mood somewhat. Especially when she offered me her toasted teacake.