I'm with Mrs Davidbowie. Kingston John Lewis is my second home and deservedly so.
Can I check I got this right OP? You had a faulty buggy. JL asked you for the cause of faulty buggy and proof of purchase how dare they manually archive records. And then they replaced it.
Then maxi cosi base was allegedly fixed by the manufacturer. JL tell you what they have been told ie it is fixed. It wasn't, the base still had a manufacturers fault, so you had to walk from the warm, clean and dry nursery section to the warm, clean and dry, underground car park and then return to the nursery section to remedy the manufacturers faulty good.
At which point was JL at fault? Asking for proof of purchase? Telling you what they had been told by the manufacturer? Or expecting you to stay in the warm and dry until problem is resolved? I'm sorry, I don't think JL was at fault.
The very same nursery section told me which door to enter during the January sales to ensure I was the first into the dept to get the biggest price reduction on the cotbed mattress they were right, the Thameside door.
A million years ago, in a galaxy far far away, my husband broke one of my precious 1 of a set of 6 Limoges porcelain plates that came as a wedding gift. I went to JL, described the plate, that they didn't even stock. They looked it up on the internet, found plate, ordered online, applied their bulk buyer discount, and passed that saving onto me.
They give unbiased views on white goods and extended warranties as the norm on any electricals. They even tell you if a product is cheaper elsewhere currently. They cannot help you enough, and if they can't help they apologise.
John Lewis are the gods of customer care of high street stores. OP, sorry you were inconvenienced but I don't see how they were at fault.