[TOMT][TV SHOW][80s/90s] A kids live-action show, set somewhere in the UK or maybe New Zealand

I don't have much information but I can remember the following:

• there was a group of kids, possibly living together or maybe just hanging out, possibly in a flat or an attic of some kind
• one of the main characters had one of those little Westy terriers or a similar type of dog
• the opening credits had said character (a boy) walking around the streets of somewhere in the UK or wherever the show was set
• one of the supporting characters was definitely called Mavis Williams, I remember that clearly
• one plot point of an episode involved the main character with the dog being convinced there was a ghost downstairs due to hearing noises
• another plot point involved a surprise party with a cake, and somebody stole a piece of the cake and tried to hide it by sculpting a replacement piece made out of toothpaste
• the Mavis Williams character got blamed for the cake mess, because she was in charge of getting the cake ready for a party or birthday