You can open multiple SIPP accounts with any number of providers and you will not break any SIPP regulations.
However, clients must be aware of the rules around contributions and the tax relief benefits they receive. Opening a SIPP account does not affect your SIPP status, but when you start making top-ups to that SIPP account, you will have begun using your SIPP allowance and benefits.
Having multiple SIPP portfolios with InvestEngine all counts as one overall SIPP account, so there is no limit on the number of SIPP Portfolios that you can open with us.