Tweedy was joined by fellow band members Kimberley Walsh, Nicola Roberts, Nadine Coyle and Sarah Harding for her hennight in London's West End on Thursday.
Letts awarded the show four stars, deciding that it "falls just short of five-star status because it is too knowing from the start - a little too full-phwoarr for the hen-night crowds".
Cruise ships with all-night bars, resorts that cater for stag and hen nights and a swimming pool area where tourists can sleep off the hangovers the next day will be winners in this type of tourism, according to the trend forecasters.