Many crowdsourcing applications require spatial data modelling to make sense of location-based observations provided by multiple users. In this context, we propose a new spatial function modelling approach to address the problem of fusing multiple spatial observations reported by possibly untrustworthy users in the domains of participatory sensing and crowdsourcing applications. Specifically, we use a heteroskedastic Gaussian process model to incorporate user trust modelling into Bayesian spatial regression. In particular, by training the model with the reports gathered from the crowd, we are able to estimate the spatial function at any location of interest and also learn the level of trustworthiness of each user. We show that our method outperforms other standard homoskedastic and heteroskedastic Gaussian processes by up to 23% on a crowdsourced radiation dataset collected during the 2011 Fukushima earthquake in Japan. We also show that our method is able to improve the quality of spatial predictions on synthetic data by up to 70% and is robust in settings of up to 30% presence of untrustworthy users within the crowd.