No, there is no minimum platform fee at present. 

However there is a minimum product fee for Pensions.

For Pension Accumulation there is a fee of 0.05% with a minimum of £12 + VAT (per annum) & a maximum of £48 + VAT (per annum).

For Pension Decumulation* there is a fee of 0.10% with a minimum of £12 + VAT (per annum) and a maximum of £120 + VAT (per annum)

See here for more information on this.

*Once you have taken any income from your pension via FAD or UFPLS the entire pension on platform will be charged the Pension Decumulation rate. The fee is taken from the pension account with the largest holding.