New EU Roaming Laws

I don't think you'll have a problem. I do all my banking online, in both Spain and in the UK, and have my UK mobile and Spanish landline registered with Sabadell in Spain and Intelligent Finance in the UK, and have no problems accessing and managing both accounts, including receiving Sabadell transaction alerts to my UK mobile.

My UK mobile is Pay As You Go with GiffGaff, £5 per month for 100MB 4G data / 125 mins / 500 texts, but I never use it all, as I mostly text and call for free via WhatsApp.

As I live permanently in Spain, I have a Telfy package which gives me internet (for TV and computing), landline and Spanish mobile for Euros 42 (including IVA) per month. The landline includes free calls to any other European country, which you select at the beginning of your contract, so I chose the UK. I could abandon the UK mobile and use the Spanish one instead, but I've had the same UK mobile number for 20+ years (rare, I know!), so more than happy to pay £5 per month to keep it - and include a little post-Brexit contingency planning perhaps....

What is OTC?

I thought that was the case;

You said;
With all respect Valenciasman if you didn't use cryptic language and read previous posts you will see that I have already confirmed we carry out all our business, both electronically, technically and physically using one UK mobile. The point you make is??
Why advise me not to use cryptic language and read previous messages when you dont understand. OTC is One Time Code, used by banks to send a code to mobile phone for a money transfer. I use them a lot.

Just checking. As previously stated we use UK mobile for ALL dealings where necessary in Spain including OTC!