is cap 1 still 4% cashback on the first 3 months?

No it's ended.
You can get 5% with Amex (plus quidco cashback) but Amex is not accepted everywhere, so depends where you do your shopping.
Tends to be accepted by hotels, petrol stations, but not by smaller retailer, cut price places (e.g. aldi) or some on-line stores.
Where there are charges they are usually higher for Amex.

Still I'm going to do it as I think it can still be very worthwhile.

Be aware that if you use it on paypal then you are charged in $s and there is a 2.73% commission charge but you'll still be in profit after 5% cashback.

Amex refund this charge automatically

Is that just for payal?
Does it show as an explicit refund.

Thanks for the info.
It's a while since I used it on paypal so they must have changed it.

One thing to watch out for though, is if you buy an item via ebay that is priced in US Dollars.
I won something that was priced in USD, but had the option of being charged in £ sterling, which I did. I paid through Paypal in UKP with a UK Amex card, but unusually the charges weren't refunded automatically.

It appears that the fact that either the seller was from the US, or the original price was in USD confused the system somehow, (in effect over the whole transaction the payment went from pounds to dollars then back to pounds then back to dollars again!) and it didn't credit the charges.

I phoned Amex though, they were very helpful and immediately applied a credit to my account manually for the charges.