For the past couple of years I've used Post Office with online order for local pickup. Very good rates if you have over £500. Plus I've also got a Post Office credit card that lets you get currency from them on a credit card with NO cash fee. So get another 6 weeks to pay for it if I time it right . AND I got £50 from topcashback for taking out the card (although this offer has gone now I think).
I always use Travelex and pick up the currency from the airport. Always order online before you get the airport, significantly better exchange rate and it's all ready counted ready for you to collect it. You tell them where you will be collecting it. Found them quick, easy and good rate.
I have used Travelex and ordered online. You can have it delivered free or pick up at Travelex shop including airport. This summer I used a local Thomas Cook. I enquired about rate which seemed ok so said I would go ahead. I mentioned that I would need to go and get money from the bank which was just next to the travel agent. The agent told me I could pay by credit card. Being wary of credit card fees I asked if it would incur charges to be told it wouldn't. It was only when my credit card bill came in at the end of July I discovered what a big mistake this was. I had a cash handling fee of £29.81 and interest of £14.68. It turns out when I phoned credit card that it had been put through as a cash advance. I am really annoyed as I never pay interest on my credit card and I had money in my bank account I had been planning to use. Anyway when I spoke to the manager at Thomas Cook I was told it would have been pointed out. Well no - for if it had I certainly wouldn't have proceeded with the transaction. You live, you learn! I will be going back to using Travelex in future.