It’s not just on Bake Off where soggy bottoms can be a problem, anyone trying to grow Courgettes can suffer from the same problem. Indeed it's not just specific to Courgettes, any plant which is a member of the Cucumber family (Marrows, Pumpkins, Courgettes) suffer from this infliction.
Caused by the flowers getting wet at the time of pollination the fruit which forms develops a rotten base, which spreads up the fruit ruining that specific piece of fruit. More of an issue on outdoor grown Courgettes and Pumpkins than on polytunnel grown - due to rain dampening flowers.
There is little we can do to prevent this ailment as gardens, the best course of action is to regularly inspect your crop, and with a sharp knife just cut off any fruit showing signs of a soggy bottom as early in their formation as possible - this stops the plant wasting energy on making this afflicted fruit any larger, and instead can concentrate on producing more female flowers - which in turn may have better luck with the weather. Regular feeding is also important, giving your plants a weekly shot of Comfrey fertiliser or tomato food will help the flower production.
In Polytunnel production keeping the water of the flowers is easier, as you mainly have to focus on watering soil and not plants when you're irrigating, but from time to time you can still get the odd soggy bottom fruit, this is caused by the condensation within the tunnel. Just do the same as outside, cut off and feed the plant.
In general Courgettes are a really productive crop, and a real seasonal summer crop, however a big courgettes is not a marrow, indeed a marrow is a different botanical vegetable. Courgettes are best harvested when 5-7” in length, at this stage they are easier to work with and have better flavour - 15” courgettes are tough to cut, hollow on the inside and you have the awkward seeds to remove too! One plant grown in a Polytunnel can produce more than 50 of these small courgettes, outside you should get around 20 per plant, so weekly harvesting should be part of your garden plan. Cucumbers are the same, regular harvesting of small fruits is advisable.