NI Credits for the period before immigrating to UK

I was working out of UK prior to 2014, immigrated to the UK in 2014 and has been in full time employment in UK since then. I have now completed 10 full years of national insurance contributions and that has made me eligible for minimum state pension whenever I reach state pension age. As, to be eligible for full state pension 35 full years of national insurance contributions are required, I would need 25 years of additional contributions from hereon. Given my current age, I will fall short of that even if I work upto the retirement age. So, I was wondering if it would be possible to buy national insurance credits for the period prior to 2014 (When I worked out of the UK) to be eligible for full state pension. Please guide.

Hi,
You are unable to contribute national Insurance contributions voluntarily before the date you officially entered the UK.
Any previous countries liability will be with them for an equivalent pension in their state.
This means you may not be able to reach the maximum UK state pension.
Please call the Department for Work and Pensions - International area to discuss your overseas involvement to the UK on +44 (0) 191 218 7777.
Thank you.